We had this problem  and worked with Microsoft support to come up with a
workaround to resolve this problem. For us it occurs whenever our SPS 2001
server is rebooted.

The solution is basically going into IIS and toggling a properties value from
the Forms folder  of the workspace where the error  is occuring but needs to be
done to each workspace because all are affected when the server is rebooted.

I have attached a workaround document  with step-by-step instructions. This
method worked for us so I'm hoping it will work for you.

If you have any questions or need further assistance please let me know.