As if Now In Tally 9 , and Tally ERP 3.7 Also One If you selected any U O M In Item and If You Passed any entry , Than You Cant Change the UOM In Item Altration Screen , If You wants Change You Need Deleate the Voucher and Than Your Currser Will move to the UOM Colomn , and In Tally This issue has Been Noted It will get Updated In Fourth Comming Release ,