Writing a custom error in SQL7 SP

Hi All, I have written a bulk upload DTS package from comma delimited text files into a SQL7 database. Occasionally an error occurs where a date is expected and one is not supplied. This causes a convert error, ie converting varchar to datetime. Ihave put error trapping code around all the necessary areas, with transactions. I need to raise an error to either the system log files of SQLs log files, however, when a this convert error occurs the procedure does not get to error trapping code where I use raiserror with severity 25 to try write to the log file. Is there a way to write an error message if this error occurs, as I can not tell if the SP updated correctly as the sp does not raise the error to the DTS package.