Well, I started randomly having Steam report:

Steam.exe (main exception): CMultiFieldBlob(pSerialized): Partial field header at end of record

This happened after windows froze on a lockup during shutdown…  The system froze on Shutdown, and it didn’t complete shutting down after 10 minutes…. I was forced to force a power off…

To solve this problem:

1. Exit Steam
2. Delete your clientregistry.blob file
3. Reboot your pc
4. Log back into Steam and let the file recreate itsel

No data is lost, and everything seems to be working fine now…

via Steam problem.. please help.