[YouTube-API] clientlogin works on one location/ip, not at another

I have a problem logging using https://www.google.com/youtube/accounts/ClientLogin. To test things (I use the Python gdata library) I constructed a curl request wich works fine at home, but on other locations I get an Error=BadAuthentication Info=WebLoginRequired error.

When I try another account this works on some locations/ip's but not on other.

How can this be explained? I use the API on ec2 instances and sometimes it works, sometimes it doesn't work.

The request looks like this: curl --data "Passwd=password&source=servicename&service=youtube&Email=info%40test.com&accountType=HOSTED_OR_GOOGLE" https://www.google.com/youtube/accounts/ClientLogin

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