It could be an MT4 implementation bug with that particular broker. If it does not disappear by reinstalling, contact the broker and inform him about the problem - send him the small EA. Any EA that uses the IsDemo function won't work on that MT4 implementation.

If the broker does not solve the problem soon, just tell him you want now to withdraw the $8000 from your real account laugh.

You can still test the MT4 plugin - just open an MT4 demo account with any other broker. There are hundreds of brokers with MT4 accounts, and opening a demo account is a matter of a minute. You'd have to install a second MT4 version, though.