I have designed a number of forms in Infopath 2003 for use by our staff that
are used on a regular basis and often by several users at the same time.  All
the forms are designed to submit to a Sharepoint Form Library and I'm finding
that many users are encountering an intermittent error when they try to
submit their completed forms.  

The error reads "The form cannot be submitted to the following
location:...The site may be offline, read-only, or otherwise unavailable.  
Unspecified Error"

All users have the correct permissions to be able to add items to the form
library and the problem seems to be occurring when multiple users are using
the same form.  My IT department is as confused as I am and I haven't seen
any other posts regarding this problem.  Does anyone know if this is a
problem with Infopath (e.g. Infopath cannot have multiple users in the same
form at the same time) or is it likely to be a problem with my forms?

Any help or suggestions would be hugely appreciated as I'm at a total loss.