Adobe reader could not open #####.fdf because it is either not a supported file type

We have a Flex based form which produces a PDF report. For most users the report displays without issue. We've recently upgraded from CFMX 6 to CFMX 7. Since the upgrade we have a few users who are getting a "Adobe reader could not open pa034925.fdf because it is either not a supported file type" error on one particular form. The users say the form used to work but now it gives them the error. In checking with them they have both Adobe Reader 6.0 and Adobe Writer 6.0 installed on their PCs. They can't uninstall Adobe Writer.

Does anyone have any ideas for this issue?

We run a multi-server version of CFMX 7.0 on Solaris 2.8.

Thanks!