Visual Web Developer markerar upp "cont2" (som att det vore felstavat)
Element 'cont2' is not a known element...
Googlade lite och hittade detta inlägg, med tanke på svarsfrekvensen så ser det dystert ut... :)
Hittade även ett där det stog:
1. This is a known bug.
To verify the problem can you make sure you have used same casing in Register tag and <userControl: attribute tag?
2. This is because your class name and control id are same. If you donot use form id delete it otherwise you need to rename this.