Just worked on a case with one of our PSS engineers at Microsoft.
The customer had Visual Studio 2005 Professional installed. When trying to apply Service Pack 1, they ran into this issue:
MSI (s) (B0:7C) [11:19:50:957]: Product: Microsoft Visual Studio 2005 Professional Edition - ENU -- Error 1331.Failed to correctly copy link.exe file: CRC error.
After going back and forth with the PSS engineer and the customer, it turns out their cabinet.dll file under \Windows\System32 was way out of date. It was version 1.0.603.0. Replacing that with a newer version (5.1.2600.2180) fixed the problem.
I'm still not sure how they got an older version on the machine but in case you run into this issue, check your cabinet.dll file.