I fixed it with Marks help
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So I have done more hunting into this error... Checked a few things...
Go to this location
C:\Users\%ENTERYOURUSERNAMEHERE%\AppData\Local\Microsoft\Report Builder
Delete the user.config file...
Open Report Builder... Fixed.
It looks as though when Report Builder crashes, it can corrupt your user config to the point whereby the .NET Framework gives you the finger and phones it in.
Hopefully this is a resolution.
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Ty for your efforts!