There was a very subtle bug in the interaction between XOTcl and the most recent versions of Tcl (8.4.14 or 8.5 from Tcl sourceforge CVS head) which costed me much grieve this week. Under certain conditions (in particular some shimmering, proc definition and upvar) it was possible that a Tcl_Obj (elementary structure in the Tcl implementation) containing the byte-code of XOTcl methods was freed and/or replaced without XOTcl noticing this. Needless to say that the bug showed only up in complex cases, i was not able to reproduce it outside of aolserver.
I can't blame this as a bug in Tcl, so i had to do a substantial rewrite of some parts of XOTcl (most dominantly, the relation between filter methods and classes). So, if one is using Tcl 8.4.14, one is required to update XOTcl to 1.5.3 (see http://www.openacs.org/xowiki/en/xotcl-core)
Maybe this is related to malte's strange problems in http://www.openacs.org/forums/message-view?message_id=500834 since he recommends in his installscript for aolserver 4.5 Tcl 8.4.14.
