When using additional map drives within PXE > MapDRV.bat. The file is Read only. Need to add additional drive mappings Manually.
All Edits should be done through the PXE configuartion utility in older DS builds. To make sure the paths are correctly setup verify under D:\Program Files\Altiris\eXpress\Deployment Server\PXE\MasterImages\MenuOption129\BDC\shared.
Save any changes and re-create the PXE DOS managed boot file in PXE Configuration utility.