Error: Unable to add this class - term maximum exceeded. Adding this class would exceed the maximum number of units or courses allowed for this term
I keep getting this message even though my units added all together are 30 units. I enrolled in both of my terms separately. This is a 3 unit course. I have a total of 2 full year(6unit) courses and 18(3unit) half year courses.

Maybe 30 units is the max you can enroll for in your program. You can check the undergrad calendar for details to double check. If you want to go over, email your department and they should be able to give you permission.

Not sure what you mean when you say you enrolled in the terms separately. But if your terms are unbalanced (e.g. 12 and 18 units rather than 15 and 15), that could cause the error.