Unable to update the series

Hi all,I am facing an issue while Updating a series from back end.
The scenario is I have 3 companies and the invoices generates with its abbriviation recently i have to change the series for opening invoices and set it like abbr.-OI- and normal series was abbr.- ,while importing opening invoices it tooks normal series for 20 records …i am trying to change the series with the update command…it says…Capture5