I believe this is a bug in unpatched HTTT. In the Westernisation Decision file for Muslim tech, it reads that you must have a neighbour that is both in the Western and Eastern tech groups, which is impossible as a nation can only have one tech group.
Go on the Paradox Forums, create an account there, register your game, and download the 4.1 beta patch there. That should fix the problem.
Otherwise, if you just want to fix this issue and not bother downloading the beta patch. Go into your EU3 folder, go in decisions, and open westernisation (notepad). Find section that relates to Muslim westernisation, and replace it with this:
[Sidenote: I believe the reason why it's bugged is that the bolded two lines in there arn't present in 4.0. Though i'm not sure if they're simply not present or something else is there.]