Function modules for lock object & could not be generated

What causes this issue?

The function modules could not be generated for a lock object.

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?

Two function modules are generated for a lock object. The names of the
function modules are ENQUEUE_<nnn> and DEQUEUE_<nnn>, where <nnnn> is
the name of the lock object.
Program XDDENQAC newly generates these function modules for certain
lock objects because the function modules generated previously would no
longer satisfy a stricter ABAP/4 syntax check. For this reason, not
only the individual function module, but the whole function group will
no longer function correctly, which could cause abnormal program
termination as soon as a program requests an enqueue lock.
You should therefore try to activate the lock object in the ABAP4
Dictionary. (The function modules are also regenerated at this time).
If there is an error, further information about the error situation can
be found in the activation log. One frequent error is that due to
subsequent changes to the key, the key fields of the primary table are
not included in the lock object as lock arguments.
Correct this in the ABAP/4 Dictionary and activate the lock object.
You can also try to delete both function modules manually in transaction
SE37 as user DDIC. You might then get information about whether
locks exist for example on the function modules.

Error message extract from SAP system. Copyright SAP SE.