My Sharepoint site is using a custom Masterpage.
I get an error just checking out, and saving the Masterpage without doing any changes.
When I open the masterpage in sharepoint designer, and try to save it, I get the usual "Site Definition Page Warning" about "Saving your changes will customize this page so that it it no longer based on the site definition".
When I press Yes, and try to access the site; I get an error about
"The control type 'bla.bla.Helpers.CSSLinkControl2010' is not allowed on this page. The type is not registered as safe."
How is it possible to get an error just by checking out and saving (without doing changes).
I also get the same error when I make a new custom masterpage and uploads it.