The verification of certificates fail if there are different CAs with the same
name installed.

For example: The command "gpgsm -k --with-validation" returns the error message
"gpgsm: certificate not found: Mehrdeutiger Name" in such a case. I do not know
which error message exactly would appear in a not localized version, but
"mehrdeutiger name" means "ambiguous name".

The error occurs only after a refresh of the CRLs. As long as a valid CRL cache
is available, the certificates are corretly verified. Therefore I assume that
the problem is related to the CRL check.