In the General Postings posting screen for TOC's there is a Disbursement YES/NO drop down box. If YES is not selected it will not be possible to write off the TOC at a later date.
If the TOC has not been flagged as a disbursement and write off is required the following procedure will need to be followed:
In General Postings create a new TOC, being careful to select the Disbursement drop down box as Yes.
Create a new WO posting applying against the new TOC.
Post a TCO posting, allocating against the original non-disbursement TOC