The payroll parameter must be set to "N" (No) in field 4 for posting to the GL in order to access the part of field 6 needed to make this change.

1.  Go to Payroll>Setup>Payroll Parameters, type C to change, change field 4, change "Ledger Post" to "N",  press Enter until the top says, “Enter field to be changed (0 to accept)”, type in a 0 and press Enter to accept, ESC, and E to end.
2.  Go to Payroll>Setup>Historical Data Items, do a C to change, type in the data item you want to change, press Enter, change field 6, change Post G/L to "N", press Enter until the top says, “Enter field to be changed (0 to accept)”, type in a 0 and Enter to accept, ESC, and E to end.
3.  Go back to Payroll>Setup>Payroll Parameters and reset field 4 to "Y" (yes) for posting to the GL.