Nils - I have had exactly the same problem so I was interested to read your post.
I did niot post anything specifically on the Forum as the cause could not be pinpointed and my other thought was anyone with the same issue would be unlikely to be able to report it or see the Forum contents of any post unless they eventually decided to try a VPN!
- It has now occurred to me twice.
- The first time I exhausted every approach(PC diagnosis, system diagnosis, router, service provider, setups etc) to try and fix the error, and eventually was able to establish it was not my PC setup or anything on, not the service provider, etc.
- The service provider investigated and had a similar issue.
- The error affects only PM.com - no other site.
- I have never had an error like this before - even with another site.
- The cause remains unknown.
- I too was able to get a workaround using a VPN.
The interesting thing is in both cases the error corrected itself. In other words all of a sudden without changing anything, I was suddenly able to log in as per normal without the VPN.
So try to log in from time to time.
The latest issue I had lasted until, about 10 days ago - all is fine now.
Do not waste further trying to troubleshoot anything - I am certain after the exhaustive analysis and work I did it is not your system or set-up or provider.
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Dave - thanks for your input here. Did everything you mentioned (and more) to no avail!