If you are using Mac OS 7.6, try to go to the Chooser. If you are unlucky, you may get an error message that says "Application unknown has quit unexpectedly, error 1010." It may happen immediately, or after you do something such as select the AppleTalk option. Four readers initially reported this (Guy Teague, Marc Beauchamp, Mike Berg and Jim). Others have since confirmed it.
Update: Most instances of this problem are due to the Control Strip module OT/PPP Strip. Disabling or removing the module should eliminate the problem. There is an OT/PPP Strip web page that documents this. (Thanks, Michael Tiffany and Alden Thatcher.)
If this doesn't solve it for you, other suggested culprits have been suggested. These include Norton Utilities, Ethernet software or hardware, the AppleScript extension (Mark Hattam) and updating to Drive Setup 1.2.2 (Bruce Baker).
By the way, according to the MacErrors utility, error 1010 is a "DS error which is specific to the new runtime model introduced with the PowerPC."