Edit Topic not displaying

I have just upgraded to 1.5 and when I go to the edit topic section the Edit box does not display.
The header and footer displays fine but no sign of the edit box.
Also My account displays a blank section where the info should be and the Global setting do not display either.
The errors on the individual pages show sys in webconfig not defined not sure if this is related though.
Any ideas please??

Problem resolved. Ajax Issue.

Can you please explain how the problem was resolved. We are also having similar issue when we installed the site everything was working fine in the admin panel. After we went live the product pages and various pages on admin site are not displaying. We can view source and see the content there but they are not rendering.