Hi,
Unfortunately, I don't think there's enough information yet to know what the problem is or how to fix it. Have you checked the server eventviewer or the Sharepoint logs for any additional information on the error? Does your form submit to a web service, to a database? Does it use UDC files? I would definitely check the Data Connections to see if they are all pointing to the correct location. Also, before submitting, I would check if there are any required, blank fields.
Hope this helps you troubleshoot the issue. Good luck.