Recently we have come up with a lot of scenarios where all of a sudden we start getting the below error.
Keyset does not exist ( exception from HRESULT : 0x8009000D)
The error code might change accordingly but you will get the error while trying to update the application pool identity with a custom account or while trying to specify a connect as user in the basic settings of a site.
You might also get the error code
Even though the above error sometimes might not affect the existing functionalities of the sites but you wont be able to make new modifications which would involve the updating of any custom accounts.
Most of the times we end up reinstalling IIS to work around or resolve this problem.
I have noted down some of the common reason why this problem might occur, what is the underlying cause of the issue and also what are all the things we can do before trying out the last resort of reinstalling IIS. You can follow the below link to get more information on that.
Hope this helps