I believe this is happening due to a library finalization ordering issue. We assume that libraries are finalized in reverse dependency order--in this case, since libcom_err uses libkrb5support, we assume that the libcom_err finalizer can call libkrb5support functions and have them work (because libkrb5support finalizers won't run until afterwards). If AIX cannot provide this guarantee, the simplest workaround is probably to disable library finalizers on AIX, at the cost of leaking a little bit of memory if the krb5 libraries are repeatedly loaded and unloaded. To do this, try removing the line "use_linker_fini_option=yes" from the *-*-aix5* branch of src/config/shlib.conf.