Geert, what version of tcl are you using on the affected boxes? Discussion on the AOLServer list (http://news.gmane.org/gmane.comp.web.aolserver) suggests that this may be a problem with tcl 8.3.x. Or maybe with glibc. Dossy wants people to post this info about their systems:
1) ns_info version
2) uname -a
3) glibc version
4) info patchlevel
If you're going to move your sites to AOLServer 4, what are you going to do to replace Jerry's nsvhr/nsunix? Use pound? The default config file in OpenACS 5.2 appears to work fine for 3.2.5 sites with only minor modifications (including sourcing your specific instance's config file), so for a single site there is little reason not to move directly to AOLServer 4. But what is the best way to handle virtual hosting for multiple sites on the same server box?