Hi,
If you are still facing the issue,
You can break the formulas as below, and try in last formula, i know no point in elaborating the formulas but some times it works..
Create Int conversion seperate,
Create String conversion seperate. and Create leftstr seperate formulas, and in final try your desired requirement formula you can consider the (fiscalmonth -1...
I have faced such issue in SP 1.8, but the above way breaking the formula worked for me...
Dont know exact reasons behind it...
Hope it helps.
Cheers..