The following example generates such an error due to the end of the range in the second PERFORM statement:
$set ilshowperformoverlap
...
perform a thru c.
perform c thru b.
goback.
                  *>  Errors are displayed as follows:
a section.        *>  COBCH1663E Overlapping perform range: 2 entries
display "In a".   *>  COBCH1664E    perform range: a thru c
b section.           
display "In b".
c section.        *>   COBCH1664E    Perform range: c thru b
display "In c".   *>   COBCH1667E       perform range end before start
go to a.