Bind9.5.1b1 Error-critical: exiting (due to assertion failure)

[iman]

Hello
I have bind9.5.1b1 on solaris9. when i start named,everything is ok
and server work properly.
but after some hours (48 h or 72 h mybe it is random!) it returns this
error in log and named process stopped!
so i must to start it by hand.
why this happened? and whats the solution?

09-Sep-2008 12:09:49.694 general: critical: resolver.c:5617:
REQUIRE((((query) != 0) && (((const isc__magic_t *)(query))->magic ==
((('Q') << 24 | ('!') << 16 | ('!') << 8 | ('!')))))) failed
09-Sep-2008 12:09:49.694 general: critical: exiting (due to assertion
failure)

12-Sep-2008 21:12:09.836 general: critical: resolver.c:5617:
REQUIRE((((query) != 0) && (((const isc__magic_t *)(query))->magic ==
(
(('Q') << 24 | ('!') << 16 | ('!') << 8 | ('!')))))) failed
16-Sep-2008 21:12:09.836 general: critical: exiting (due to assertion
failure)

Here is my named.conf:
options {
        version "version not currently available";
        pid-file "/opt/namesurfer/run/named.pid";
        directory "/opt/namesurfer/named/namedb";
        dump-file "/opt/namesurfer/named/namedb/named.dump";
        max-cache-size 310m;
        recursive-clients 32768;
        statistics-file "/opt/namesurfer/named/namedb/statistics";
        tcp-clients 10000;
        allow-recursion {
                any;
        };
};
logging {
        channel simple_log {
                file "/var/adm/named/bind.log" versions 3 size 50m;
                print-category yes;
                print-severity yes;
                print-time yes;
                severity warning;
        };
        category default {
                simple_log;
        };
};
controls {
        inet  127.0.0.1 port 953 allow { 127.0.0.1; } keys
{ "rndckey"; };
};

Regards