Timetable Scheduling - Solver error

Help needed.

I am trying to schedule a timetable (by optimizing the total no.of students common across various subjects).
5 slots on each day (6-day week), which gives me 30 slots ( 30 subjects are to be assigned with two slots for each i.e. 60, maximum of 2 courses can be assigned for same slot).

I am using 30x30 binary variables (1-if the course is assigned for that slot, 0-else), effectively 900 decision variables.
Since excel does not support more than 200 variables, i am getting this error 'too many adjustable cells'.

is there any way to overcome this problem??

Thanks in advance

can someone help me with this!!