Assuming it did once work okay, then sometimes the c:\windows\setscan.ini file which is used by the Canon ISIS and TWAIN drivers becomes corrupted and this causes the Canon TWAIN driver to stop working with EzeScan.
Try the following:
Rename setscan.ini to setscan.old
Reload EzeScan and run a job (that uses this scanner)
You will get a prompt for a scanner model, select your scanner in the drop down list.
Test that the job runs ok.
Load EzeScan and try the job again.
Contact EzeScan support if the issue is still occurring.