Actually the above sql will work but needs the following changes:

Select max(seq_num) + 1

From (Select seq_num = Right(your_col, Len(your_col) - @len_first_part)

      From Your_Table

      Where Left(your_col, @len_first_part) = @first_part

      And   Isnumeric(Right(your_col,...

I think this may have to do with the MSDTC service running (or rather not running) on your client's server. Check if it is running and start it if it...