Has anyone ever been on MUGSI before, finally seen that their class is available, only to be informed that the core is full? I thought if this was the case, the class was full and unavailable.

Yes. Probably that it is still available (i.e., there ARE spaces left for students) but it's not available for your specific year (because there are only a certain amount of seats allocated for others years).

That's my best guess anyways.

My second best guess is that Solar is a piece of shit from the stone ages.

Wow that must have been disappointing. It could be either of the things Cheri mentioned, my guess would be that you'll never know

Relevant

Thats happened to me before, I just called the school and they fixed it up ( on their end it showed, available and not full so they couldnt understand my problem but they put me in the class)