Capture: normalize.exe problem

We have developed an application to convert TIFF files to PDF files using
"normalize.exe" and "collator.exe" programs from Acrobat
Capture 3.05.

"Normalize.exe" and "collator.exe" programs are called using
a command line like this:
 normalize -comp TIFF image.tiff

The application runs fine and we used it without any problem.
Recently we modified the application to be able to run more than one instance of
it on the same computer. The application itself runs fine but we have many
errors with the "normalize.exe" program. These problems occur when
more than one instance of "normalize.exe" run at the same time. A 0
byte length PDF file is generated and the log file contains the message:
"Abort: image.TIF [Convert Image to PDF]: Unrecoverable error processing
the file"

This is an intermittent problem and when it occurs we just execute the same
conversion and it works fine. On a multi CPUs computer the problem occurs much
often than on a single CPU one.

Does some one knows about this problem and how to solve it?

Thanks,