from the Apple Tech Info Library: http://til.info.apple.com/techinfo.nsf/artnum/n24431
During startup the computer presents a dialog box with Error Type 41. The computer stops responding and the desktop never appears. The same thing happens even if extensions are disabled.
Error Type 41 is not new and is not unique to any version of System 7, Mac OS 8, or Mac OS 9.
This error means "can't load the Finder." If you receive this error message it is likely that the Finder has been damaged. Deleting the Finder and reinstalling it should correct the situation.Performing a clean installation of all the system software is not necessary unless simply reinstalling the Finder does not work.
Reinstalling the Finder is done by removing the Finder and performing a simple installation of just the base system.
Locking the Finder (in the "Get Info" window) may prevent the error condition from recurring. However, be aware that a locked Finder can cause some system software installations to fail. If using Mac OS 8, upgrading to at least Mac OS 8.1 may help prevent one cause of this issue.
If the error occurred immediately after installing some software, there may have been a failure during installation or you may have some incompatible software. Any time you are reinstalling software to correct an error or behavior, you should run Disk First Aid beforehand and repair any damage found by Disk First Aid.
To read more about performing a clean installation of system software, please see article 30691: "Mac OS: When & Why to Perform a Clean Installation"
Hope this helps!