Apple is still signing the 5.0.1. The reason you get the error is because:
- Your hosts file is pointing to Cydia's servers.
- TinyUmbrella is pointing to Cydia's servers.
Make sure iTunes can talk directly to Apple and the error will disappear.
As of this moment Cydia will not back up any IOS 5 blobs. When you get to 5.0.1, use
iFaith v1.4.