I recently had a problem getting the Konica Minolta Twain Driver for the C253 scanner (among others) to be recognized by the twain device manager, and thus it was not listed as one of the twain devices available, either in PhotoShop or in Atalasoft DotTwain. The nice people at our local Hughes Calihan Konica Minolta here in Phoenix helped me figure this out, along with Lou Franco of Atalasoft (see his comments below), and I wanted to post the solution for anyone having a similar problem.
Ultimately, the problem was that another software package (I believe it was Business Object’s Crystal Reports XI Release 2), installed a copy of the LIBEAY32.dll into the C:WindowsSystem32 directory. LIBEAY32.dll is part of the open source OpenSSL suite, and I have 18 (!) different versions on my system. They mostly live in harmony, but when the Konica Minolta twain driver tried to load, it would get the version of LIBEAY32.dll that Crystal Reports had put into System32 (since that is very early in the Dynamic Link Library Search Order — see http://msdn.microsoft.com/en-us/library/ms682586.aspx) and when the LIBEAY32.dll that was loaded did not have the proper ordinal entry point, the Konica Minolta twain driver would not be loaded by the twain device manager.
When PhotoShop loaded, it would emit an error message about the missing ordinal in LIBEAY32.dll; when File/Import was pulled up in the menu, the Konica Minolta twain device would just be missing, and there would be no error here.
Compounding the problem was that my test application using the Twain source manager via the Atalasoft DotTwain ShowSelectSource() function did NOT issue any error.
However, a test application I made with Visual C++ loading the Twain device source library for the Konica Minolta scanner did produce the error.
It turns out that the only difference between my test application and Photoshop was the SetErrorMode() function, which sets the process’ ErrorMode. You can call GetErrorMode() and SetErrorMode() following these imports:
private extern static uint SetErrorMode(uint mode);
private extern static uint GetErrorMode();
If you then call SetErrorMode(0) before the Atalasoft ShowSelectSource() function, the user DOES see the error messages from the operating system. However, the Twain Source Manager twain_32.dll does not return any error code to ShowSelectSource(), so obviously ShowSelectSource() cannot return any error code either. As noted below, the only way for a calling program to get an indication that a source did not load is to call the twain source DLL directly rather than through the Twain Source Manager, and observe that the LoadLibrary call returns NULL.
Having figured out that the problem was that the Business Objects LIBEAY32.dll was in the System32 directory, the solution was a little difficult. The Konica Minolta Twain Driver worked once the LIBEAY32.dll was removed (or renamed) in System32, but Crystal Reports XI Release 2 tries to repair it’s installation if if finds that file missing.
However, by placing the LIBEAY32.dll from the Konica Minota twain driver directory (in a subdirectory of C:windowstwain_32, where the twain device files live) into System32, both the Konica Minota twain driver and Crystal Reports seem to be happy. For good measure, I put a copy of the LIBEAY32.dll that Crystal had put into System32 into Crystal’s own directory (since that has higher priority in the .dll search order) so that Crystal should load its own LIBEAY32.dll
For reference, I tracked down the problem by making a test Visual Studio C++ app and trying to load the Konica Minolta twain device driver (mostly from http://msdn.microsoft.com/en-us/library/784bt7z7.aspx) :
Then, in the click handler:
HINSTANCE hDLL; // Handle to DLL
UINT uErrorMode = SetErrorMode(0); // so you get an error message from the OS
LPCWSTR str=L"C:\Windows\twain_32\KONICA MINOLTA\RTM_V3\kmtw3R.ds";
hDLL = LoadLibrary(str);
The LoadLibrary call produces a MessageBox (see the SetErorrMode() docs) with the error, and returns NULL, if there is a problem loading the twain source driver library. Note that the twain device driver will need other files in that directory, and you will get those errors first; you can fix that problem by adding it to the PATH for testing. The System32 will still be ahead of the PATH (but not ahead of the application .exe directory) so you will get the error message you are looking for. Also note that the twain device driver library, in actual use, will NOT need the PATH to be set; the twain device manager appears to take care of that.
Another approach that works is to change the current working directory to the directory containing the twain source driver before calling LoadLibrary on the driver, as this will more closely approximate the DLL Search Order used by the twain source manager. Again, the problem is that, although the source driver does install the files it needs into its own directory, the LIBEAY32.dll that Crystal installs into System32 is still AHEAD of the LIBEAY32.dll installed into the source driver’s directory! (see Lou Franco’s comments below) DLL Search Order is a fairly complex topic, and can vary depending on a number of factors; google “Dynamic Link Library Search Order” for info. Note that, unless SafeDllSearchMode is disabled, changing the current working directory does not change the DLL search order.
Also, when I tried this with a 64 bit version of Vista, Crystal installs LIBEAY32.dll into /Windows/SysWOW64, which is the directory that takes the place of /Windows/System32.
Regretably, when LoadLibrary fails, FormatMessage produces only a message that the operating system could not run the file. The only detailed info available seems to be the message box provided directly to the user by the OS, and only when SetErrorMode(0) is in effect.
See also: http://www.cube316.net/blog/archives/200710/147.html for a similar problem.
— Edited 12/31/08 10PM to add info about using SetErrorMode() to show the error message box, that the lack of error reporting to the application occurs at the Twain Source Manager level, to reinforce the info about DLL Search Order, and to take Lou Franco’s comments into account; Edited 12/3/09 to add info re 64 bit Vista – JMN