Make sure that the scheduled frequency of the task being created is an exact multiple of the scheduled frequency of any other existing lower frequency tasks (see mso700.cbl, search on error code 6727)
Eg
if creating task 9210 with frequency 180 days, mims checks for all existing tasks with task number like '92%' and strictly greater than '9210'.
Say it finds tasks 9220 with scheduled frequency 30 days. It divides 180/30 = 6 and this is ok. But if it finds task 9220 with frequency 91, the error will be generated. The error is generated if remainder of division is not zero, or if the result is < 2.
Suggest to check frequency of associated tasks, eg using Corvu:
select SCHED-FREQ-1 from msf700
WHERE REC-700-TYPE = my_type and
EQUIP-NO = my-EQUIP-NO and
COMP-CODE = my-COMP-CODE and
COMP-MOD-CODE = my-COMP-MOD-CODE and
MAINT-SCH-TASK LIKE first 2 char of my-MAINT-SCH-TASK and
MAINT-SCH-TASK LIKE > my-MAINT-SCH-TASK
if all such tasks have scheduled frequency that can exactly divide the current task's frequency, then MIMS may have a bug.