WIS 10901: ORA-01830 date format picture ends before converting entire input string

ORA-01830
date format picture ends before converting entire input string. (WIS 10901)
Scenarios when I
could expect this error:
Convert Date field to other
format.
Example
I want to calculate a filter
for rolling 12 months. TBL_DIMN_CALN_POST.D_PERD is my date field...