lame server resolving and unexpected RCODE (SERVFAIL) errors

server crashes, probably named / bind

[adrianTNT]

Can someone help with this?
A dedicated server goes down around twice a day, all sites become unavailable, plesk, etc.
System is Fedora with Plesk installed.
At the same time interval I get in /var/logs/messages these errors:

lame server resolving and unexpected RCODE (SERVFAIL)
and
"lame server resolving"

Feb 9 04:08:35 ffiles xinetd[2389]: EXIT: smtp status=0 pid=27348 duration=5(sec)
Feb 9 04:16:36 ffiles xinetd[2389]: START: smtp pid=987 from=94.100.176.107
Feb 9 04:16:42 ffiles xinetd[2389]: EXIT: smtp status=0 pid=987 duration=6(sec)
Feb 9 04:21:21 ffiles xinetd[2389]: START: smtp pid=5782 from=208.109.80.47
Feb 9 04:21:24 ffiles xinetd[2389]: EXIT: smtp status=0 pid=5782 duration=3(sec)
Feb 9 04:22:44 ffiles xinetd[2389]: START: smtp pid=7078 from=208.109.80.47
Feb 9 04:22:47 ffiles xinetd[2389]: EXIT: smtp status=0 pid=7078 duration=3(sec)
Feb 9 04:24:18 ffiles named[2546]: lame server resolving 'secdns.starhub.net.sg' (in 'starhub.net.sg'?): 203.116.1.93#53
Feb 9 04:24:18 ffiles named[2546]: lame server resolving 'secdns.starhub.net.sg' (in 'starhub.net.sg'?): 203.116.1.93#53
Feb 9 04:24:18 ffiles named[2546]: lame server resolving '12.95.12.202.in-addr.arpa' (in '95.12.202.in-addr.arpa'?): 203.116.1.94#53
Feb 9 04:24:19 ffiles named[2546]: unexpected RCODE (REFUSED) resolving '191.124.69.76.in-addr.arpa/PTR/IN': 207.236.176.21#53
Feb 9 04:24:19 ffiles xinetd[2389]: START: smtp pid=8098 from=72.167.218.24
Feb 9 04:24:20 ffiles named[2546]: lame server resolving '89.92.69.85.in-addr.arpa' (in '92.69.85.in-addr.arpa'?): 82.216.111.75#53
Feb 9 04:24:20 ffiles named[2546]: lame server resolving '89.92.69.85.in-addr.arpa' (in '92.69.85.in-addr.arpa'?): 82.216.111.76#53
Feb 9 04:24:22 ffiles named[2546]: lame server resolving '130.172.122.86.in-addr.arpa' (in '172.122.86.in-addr.arpa'?): 193.231.233.8#53
Feb 9 04:24:22 ffiles xinetd[2389]: EXIT: smtp status=0 pid=8098 duration=3(sec)
Feb 9 04:24:23 ffiles named[2546]: lame server resolving '36.245.243.180.in-addr.arpa' (in '245.243.180.in-addr.arpa'?): 202.134.0.62#53
Feb 9 04:24:23 ffiles named[2546]: lame server resolving '38.17.166.125.in-addr.arpa' (in '17.166.125.in-addr.arpa'?): 202.134.0.62#53
Feb 9 04:24:23 ffiles named[2546]: lame server resolving '36.245.243.180.in-addr.arpa' (in '245.243.180.in-addr.arpa'?): 222.124.18.62#53
Feb 9 04:24:23 ffiles named[2546]: lame server resolving '89.92.69.85.in-addr.arpa' (in '92.69.85.in-addr.arpa'?): 82.216.111.76#53
Feb 9 04:24:23 ffiles named[2546]: unexpected RCODE (REFUSED) resolving '38.17.166.125.in-addr.arpa/PTR/IN': 222.124.18.62#53

This particular part seems to contains "(REFUSED)", others have "(SERVFAIL)", and this appears in same time when server becomes unavailable.
This is the only named/bind related log I could find, I suspect that the named service goes offline but I am not sure, can that be the cause of the above errors?