I have a problem here:
An error occurred during the compilation of the requested file, or one of its dependencies. The type 'Microsoft.SharePoint.WebPartPages.WebPartPage' exists in both 'c:\Windows\Microsoft.NET\assembly\GAC_MSIL\MyProject\v4.0_220.127.116.11__4829610975c6feae\MyProject.dll' and 'c:\Windows\Microsoft.NET\assembly\GAC_MSIL\Microsoft.SharePoint\v4.0_18.104.22.168__71e9bce111e9429c\Microsoft.SharePoint.dll'
When I enter/create/view list item of particular content type I receive this error. I'm new to SharePoint and this error sounds for me like nonsense. When I simply save my master page (so it's no longer based on my site definition) it fixes my problem. I have none of my code in my master page.
when I return it to site definition, error gets back.
how its connected to my master page and site definition? how to fix this? because all I have for now is workaround... please help, I searched everywhere.