Using IF THEN ELSE statement in VB

I cannot seem to get an IF statement to work within my asp.net page

Error = Could not load file or assembly 'Microsoft.VisualBasic, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies.

without the IF statement it works fine.

Can anyone shed some light on what the problem could be.