Error 412 - fra e-mail link

Når jeg får e-mail fra Comon, får jeg flg. fejl på een maskine, men ikke på andre - så det er åbenbart noget på min PCer - men hvad:

Error 412--Precondition Failed
From RFC 2068 Hypertext Transfer Protocol -- HTTP/1.1:
10.4.13 412 Precondition Failed
The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This response code allows the client to place preconditions on the current resource metainformation (header field data) and thus prevent the requested method from being applied to a resource other than the one intended.