We run a lot of mojoPortal-based Web sites. Unfortunately, upgrading mojoPortal between the hundred releases per month is difficult and often unnecessary. Unfortunately, .NET 4.0 appears to break mojoPortal. It’s not a big deal to fix the issues, but they can take a while to find. Below are the changes we had to make, hopefully saving you hours or days of lost time 
If you’re having issues getting mojoPortal to run under the .NET 4.0 Runtime, please try the following:
- Bring your project into VS2010, convert it, and recompile.
- This will likely require you to check your references – System.Web.Services will likely have a broken reference. Just remove it and add it again.
- Compile the projects separately.
- In the web.config, uncomment the httpRuntime config item and make sure it looks like this:
<httpRuntime maxRequestLength="2097151" executionTimeout="3600" useFullyQualifiedRedirectUrl="true"
requestValidationMode="2.0" />
- The requestValidationMode is the big deal. Otherwise you’ll get errors whenever you post on your site.
- For the most part, the above changes worked. Once you have mojoPortal compiling (in case I left something out <grin>), the change above may be the only other change you need to make.
Please ask additional questions in comments.
Good luck!
-Auri
Auri's Blog 