Problem
User can access the website but is not logged in.
Under certain circumstances, the user can lose the Handler Mappings for *.svc files which results in the described behaviour.
Solution
Open a Command Prompt in Administrator mode and write:
On 64 bit OS:
DISM /Online /Enable-Feature /FeatureName:WCF-HTTP-Activation45
On 32 bit OS:
DISM /Online /Enable-Feature /FeatureName:WCF-HTTP-Activation
Press Enter:
Related articles