SonicWall not handing out all IPs in a DHCP Range

I had a situation yesterday where there was a run on my DHCP addresses.  It was expected and i had carved out a range to handle the additional requests.  However, Sonicwall didn't hand out all the available addresses in the DHCP range. the range was .20 to .40 and it would hand out .20, .21, .22, .23 but .24 was not issued.

It skipped on several addresses to the point where i ran out of IPs (50 addresses in the range; only 32 connected but out of addresses).  I checked the lease time and it was only set to 10 minutes. When i ping the offending IPs they don't ping back so I assume the IP is available..
Any ideas??

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i am curious.
what model sonicwall, what version sonic os?
is the dhcp scope contiguous?
bryant1Author Commented:
      TZ 170 Enhanced
ROM Version:       SonicROM

I have 3 separate ranges; 20 addresses in each range..
first thing i would do is upgrade the sonicwall to the latest OS version.
bryant1Author Commented:
OK so the story gets deeper.. I did a firmware upgrade to as recommended and still was having the same issue... I started digging a little further and stumbled upon something rather strange.  If i Go into the DNS logs, the IPs that sonicwall are not handing out are registered to a user "dave.mydomain.local", what is strange is that no user dave exist in my active directory.  Any ideas on how to find out why/how dave is getting these ips?
Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
dave.mydomain.local is no user, it is a computer name?!

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