How to fix namespace problem with autogenerated Master property if MasterType is set

Question

after weeks of having this issue I finally decided to ask for a solution to the following problem:

In the .aspx page you can set

<%@ MasterType          


        

Answer 1

For some reason the designer believes that the master page is defined in namespace NAMESPACE1, so look at the master page definition (and code behind) to check its namespace has not been modified (possibly accidentally).

If there is nothing obvious, a search in all files (*.cs, *.aspx, *.master, ...) for NAMESPACE1 may be needed.

(This is where using a VCS would help --- you could check the history of changes.)