Specify a valid value

What causes this issue?

No position which actually exists in PD (in the file PLOG) may be
entered as a 'default position', since it only displays a symbolic
position.
1. If you are editing the entry PLOGI PLOGI:
The entry PLOGI PRELI already contains a position number which exists
in the required plan version. Please cancel your entry.
Before entering the plan version, you must enter a position number
according to PLOGI PRELI that does not already exist in this plan
version.
2. If you are editing the entry PLOGI PRELI:
Please enter a value for which no position was created in the
integration plan version (you will find this in T77S0 - entry PLOGI
PLOGI); Also check whether the PLOGI PLOGI entry is correct.

Error message extract from SAP system. Copyright SAP SE.