I ran into this issue when trying to create a new connection for User Profile Synchronization in SharePoint 2010. This is just many of one of the possible causes for this error message, so be sure to check the ULS logs and the windows application event log for details.
When saving the new connection, I received the generic error:
Unable to process Create message
Event ID 6306 (FIMSynchronizationService) was also logged in the application log.
I named the connection “AD DS (forest.com)”. It turns out that the following naming rules apply:
A valid management agent name can only contain upper or lower case letters ‘a’ through ‘z’, the digits ‘0’ through ‘9’, dash (‘-‘), underscore (‘_’), period (‘.’), comma (‘,’), or space, and may not be a reserved system file name.)
Just create the connection with a name that follows the naming rules above.