Please first check if the PDF file is opening by your Acrobat application.
And if you are using windows OS, please open Windows Task Manage and check if there is task on the PDF file is running.
You can stop the related task, then you won't see the error message again.
Hello! Unfortunately, I am using a mac. Any other advice?
The general things to try are:
1) Make sure that youdo not have the file open, close any applications that might have had the file open
2) Make sure you are saving to a location you can "write" to, such as your Desktop (not a read only location)
3) Try giving the file a new name when saving (you probably need to add ".pdf" or you might end up with a file with no extension and you'd get another error message)
4) Try restarting the web browser
5) Try another web browser
6) If all else fails restart your computer and try again
This "save" process is really controlled by Flash and the operating system of your computer and is mostly out of the control of FormsCentral once the File Save dialog is shown, however there are rare cases where something about a particular form causes an issue so if none of the above steps resolves your issue please contact us and share your form so we can investigate.
See this FAQ for the latest on this issue: http://forums.adobe.com/docs/DOC-4141