Error when grouping seurity deposits

What causes this issue?

Errors arose while you were trying to summarize all securities in the
same contract account and contract (contract account only for IS-T) in
one security. The transfer posting could not be carried out without
causing inconsistencies in the data.

System Response

The securities were not changed: There are still contracts that contain
more than one security.

How to fix this error?

Check whether there already inconsistencies in the data in the system.
Correct these where necessary and restart the report. Note that
securities that have already been released are not converted.

Error message extract from SAP system. Copyright SAP SE.