When running the UltraDev Cassini Server explorer, you may run into errors with message such as "Name cannot begin with the '<' character, hexadecimal value 0x3C. Line 5, position 6.", to solve this problem, add the line

<trust level="Full" />

to the <System.Web> section of the web.config located in the Cassini Server explorer directory (e.g. C:\Program Files\UltiDev\Cassini Web Server Explorer), and rerun the explorer