Hi,
You didn't mention what version of mojoPortal. Are you using an official release or are you compiling it yourself from source code?
If you are using the official release of version 2.3.7.0, we fixed a bug something like this yesterday and we patched the 2.3.7.0 release. If you download it again and replace the file /bin/mojoPortal.Web.dll it should solve the problem.
Hope that helps,
Joe