Base class includes the field 'X', but its type (System.Web.UI.ScriptManager) is not compatible with the type of control (System.Web.UI.ScriptManager)

Question

The full error is

The base class includes the field \'ScriptManager1\', but its type (System.Web.UI.ScriptManager) is not compatible with the type of

Answer 1

Adding the section above fixed the problem on our dev machines and test server, but not our live servers.

It turns out that if your web.config file contains an xmlns attribute of xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0" then you will get a GAC conflict:

BAD.web.config


etc

but this version from the devt machine is fine:

GOOD.web.config


etc

So make sure that 2.0 reference is removed from the top of your web.config file.