I get an error when I use the following statement:

=IF(ISNUMBER(SEARCH("Cost
Center",E12)),"A",IF(ISNUMBER(SEARCH("OM",E12)),"B ",IF(ISNUMBER(SEARCH("Bank
Information",E12)),"C",IF(ISNUMBER(SEARCH("Departm ent",E12)),"D",IF(ISNUMBER(SEARCH("Promotion",E12) ),"E",IF(ISNUMBER(SEARCH("Reports
To",E12)),"F",IF(ISNUMBER(SEARCH("SAL",E12)),"G"," Not OK")))))))

The error message is as follows:
The formula you type contains an error

I think you are missing a closing parenthesis on the end of your formula.

Rick