This is a complete blow in the dark; it may not work for you at all.
In a previous project, there was a problem with the Silverlight application, which does not work for multiple users. We found a message on the Silverlight forums saying that the problem was ultimately due to a damaged user profile. However, since Microsoft closed the Silverlight forums, I can no longer find this article.
It turns out that the fix was to open a command prompt and run the following:
reg export "HKCU\Control Panel\International" international.reg reg import international.reg
Obviously, since this is due to registry modification, proper care should be taken.
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