That's not enough information to really go on, and it's typically indicative of something not being installed correctly (or corrupt) on your system. I'd start with reinstalling the first link below. If that doesn't fix it, try reinstalling .NET 3.5 (second link below). If you're not running Win7 SP1 or later, I don't really support it .. but the .NET 3.5 installer will likely be your better first-choice.
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- specifically for my program, you want the x86 installer.. but running both won't hurt anything
.NET 3.5 -
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