Surreal
sometimes that kind of thing can show up from a conflict between two different versions. For example Acrobat ver 3.0 may not always be able to open forms created in ver. 4.0 or 5.0 Your customers version of Acrobat may be part of the problem. You might want to check on your end though that the save options you are using are set to save compatible with the earlier versions.
JD