You may not claim the tuition credit if you were reimbursed or expect to be reimbursed by your employer with tax free assistance. If for some reason, the reimbursement falls thru or you have to pay it back, you deal with that by filing an amended return in the future.
By law your employer can only give you $5250 maximum, tax free. If you got more than $5250, the amount above $5250 is usually already included in box 1 of your w-2. The excess is considered your after tax money and that amount can be used to claim the tuition credit.
The course you took is not eligible for the more generous American Opportunity credit. It is, most likely, eligible for the Lifetime Learning Credit (the portion paid by your after tax money).
