& Beginning of function & or end of function & missing

What causes this issue?

You have tried to end a logical block with the function 'X'. However,
the logical block that was started with the function 'Y' has not yet
ended. Logical blocks represent the functions
IF ... ELSE ... ENDIF or
LPBEG ... LPEND.
Example:

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

IF (Function Y)
.
.
LPEND (Function X)

How to fix this error?

This situation could have occurred because:
You have forgotten to end the logical block IF .. ENDIF by placing
ENDIF before LPEND.
You have forgotten to begin the logical block LPBEG .. LPEND by placing
LPBEG after IF.
Insert the required function.

Error message extract from SAP system. Copyright SAP SE.