i have never used nsladp, therefore i have not seen the problem yet, but maybe you could find my hints still useful.
First of all, be as precise as possible in all bug reports with version numbers of aolserver, tcl, and the involved modules and libraries.
For debugging, i would recommend to recompile all involved C components (including aolserver and tcl) with "-g". Then make sure, your system configuration allows core dumps, and if the server crashes, analyse the core dump with gdb. You will get a backtrace, which might (or might not) give you a hint what happened were.
Note that the error might be in places, where you don't expect it. by googleing around i found many error reports with sig11 (http://www.google.at/search?q=ldap+segmentation). Or, maybe the library you are using is not thread safe...
