To help figure out what is happenings you could compare the log files generated by twain_32.dll when using your app and twacker.
The log file is stored in your temp folder
%temp%twain.log
Whenever you receive a TWRC_FAILURE you should do a DG_CONTROL / DAT_STATUS / MSG_GET to find out why the previous message failed.
The problem might be a sequence error. The order of capability negotiation is discussed in the TWAIN spec on p600(A-34). Transfer mode should be negotiated first.
twain_32.dll provides a method to expose WIA drivers as limited twain drivers. For best TWAIN support use the real TWAIN driver.
Regards,
Jim Watters
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JFL Peripheral Solutions Inc.
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