AX 2009 - Expense management - Attaching receipts to expense report on Enterprise portal?

I am on AX 2009 RTM version 5.0.593.0.

Can we attach the receipts to Expense reports on Web portal (Employee services -> Manage expenses -> View expense report):

 When I try to attach any document with Expense report on Enterprise portal, I get following infolog errors:

ClrObject static method invocation error.

File upload failed. File write error on server.

Is it a known issue?

Fyi, I have already configured the document management under Basic > Setup > Document management.

Any ideas??