I'm having the same problem as well.  The IRS 1120-S instructions https://www.irs.gov/pub/irs-pdf/i1120s.pdf state "If column (a) on line 2 or line 4 of the Schedule M-2 includes expenses paid with proceeds from forgiven PPP loans, an S corporation should report that amount in column (a) on line 3 and in column (d) on line 5 of the Schedule M-2. 

Line 3 is fine in ProSeries, but I can't get it on Line 5 without getting errors.
How do we input the expenses paid from forgiven PPP loans on M-2?