Are you using a 3rd paty application to convert. If yes, then you have no choice to log error.
If the application is written by you, the it is pretty straight forward to log your error.
In the code where you are transferring data to another database, by insert statement, you need to trap the catch exception. Any error, you need to update the log text file.
try{
}
catch(SqlException ex){
}
Hope this help.
cheers