Also posted to Grants.gov today is this notice: 

Statement from Adobe on Version Compatibility

Adobe is aware of several issues with Adobe Reader when used with Grants.gov application forms and is working closely with Grants.gov to remedy these issues. These problems will be fixed in a future version of Adobe Reader.

Applicants should be aware that Grants.gov forms have been tested with and are compatible only with Adobe Reader version 7.0.9. Using Adobe Reader 8.0 or 8.1 may cause the application to fail validation after submission and thus be rejected by Grants.gov.

It goes on to say that filling out the forms in a Web browser can make the packages large, resulting in timeouts upon submission if using a dial-up connection. The best advice is to use a high-speed Internet connection.