Failed to load file or assembly "system.data,version=2.0.0.0,culture=neutral,publickeytoken=b77a5c561934e089" or one of its dependencies. The system cannot find the file specified.

SQL Server 2005 opens a message that does not have normal access to data:
Failed to load file or assembly "system.data,version=2.0.0.0,culture=neutral,publickeytoken=b77a5c561934e089" or one of its dependencies. The system cannot find the file specified.

Workaround:
Open the C:\WINDOWS\assembly folder to see if there is an assembly with a name of "System.Data", a version number, a public key token that matches the version in the error prompt, and a PublicKeyToken value.
If not, drag the System.Data.dll under "C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\" to C:\WINDOWS\assembly, at which point C:\WINDOWS\ A new System.Data assembly will be generated under assembly (if there is no previous version of the Assembly), and the problem will not occur if you reconnect the database after you have finished.

Failed to load file or assembly "system.data,version=2.0.0.0,culture=neutral,publickeytoken=b77a5c561934e089" or one of its dependencies. The system cannot find the file specified.