Hi Pawel,
I'm sorry to hear that you're having problems.
I have checked the logs, and they do indeed show a large number of server errors. Normally, HttpError 400 "Invalid Value" does indeed indicate an invalid tasklist name, but it appears that the server is currently returning that error even when the tasklist name is valid.
The Google Tasks server does unfortunately misbehave from time to time, and the errors returned don't always provide much help. In this case, it would appear that the tasklist name is OK, however for some reason the server decided that it is an "Invalid value". Then, the next day, the same value will probably be accepted.
There is a total daily limit of 100,000 tasks, but yesterday GTI only processed 21,000 tasks, so I don't believe that is the issue.
I'm sorry that I can't offer any further help. Unfortunately, the Google Tasks server is out of my control ... I have
logged an error with Google
Regards,
Julie