Slitherine

When I try and start FoG I get this message:

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Runtime Error
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Runtime Error
Press OK to Continue
Press Cancel to Quit.

Please report what caused this error
along with the information below.
..\..\..\..\Common\plugin.cpp: 7458
Failure Condition: pluginEntryTable.GetEntry( entrypointName, out )
can't find plugin method DecodeBase64(data As String, encoding as TextEncoding = nil) As String
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OK Cancel
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And that is as far as teh game gets- i am using windows 7

Uninstall the game and install it in a different where the game was previously installed (for example C:\Slitherine\FoG).