Please check release classes (see long text)

What causes this issue?

Here you can assign release groups to release classes. Only one release
class should be used within the release groups for overall release and
the release groups without overall release in each case. However, in
this instance several release classes have been used.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Assign the release groups that were created for overall release to one
release class only. Assign the release groups that were not created for
overall release to a different release class.
Example:
Rel. group,,Rel. obj.,,Overall rel.,, Class ,, Description
01,,1,,_,, FRG_EBAN,, Group 01
02,,1,,_,, FRG_EBAN,, Group 02
S1,,1,,X,, FRG_GF_EBAN,, Group S1
S2,,1,,X,, FRG_GF_EBAN,, Group S2

Error message extract from SAP system. Copyright SAP SE.