according to MacFixit.com:
ATM and ATR are not the only significant software that is currently incompatible with Mac OS 9. Other confirmed conflicting programs are Stuffit Deluxe, Suitcase, MasterJuggler, Norton AntiVirus, Norton Utilities' File Saver and Virex 6.0 (but apparently not 5.9).
For example, readers noted that Virex (the control panel and perhaps the Scheduler extension) causes a bus error crash at startup. A couple of readers found that MindExpander worked in situations (primarily when trying to expand .sit files) where StuffIt would fail.
Apple has RECENTLY removed some API's from OS9 and that breaks some softwares..
and this, from
Apparently Apple have moved or deleted an API in OS 9 that allows several well known and/or essential extensions to operate. Therefore until these extensions are modified/patched they will crash the computer or not load.
The most important of these extensions is any version of Adobe Type Manager (ATM, ATM Light and ATM DeLuxe). As it is virtually impossible/very difficult to operate a computer using PostScript Type One fonts without ATM, users everywhere who jump in and install OS 9 could be in for a very rough time.
The other major extensions known to have problems are-
Norton Utilities File Saver
[This message has been edited by wlonh (edited 10-01-1999).]