Network connections being dropped

We have been receiving reports from users connected to a specific switch that they have been being dropped off of the network for anywhere from one minute to 5 minutes.  I have checked the Cisco switch that they are connected to and have found a couple of errors.

entry number 22 : C4K_L2MAN-6-INVALIDSOURCEADDRESSPACKET (Suppressed 11 times)Packet received with invalid source MAC address (00:00:00:00:00:00) on port Gi1/1 in vlan 173 timestamp: 149635257

The port that is reporting the error, Gi1/1, is the connection between this switch and our core switch.  The other issue that I have seen is in the DHCP tables for these users.  I have noticed that some of the clients connected to the switch have multiple entries in the DHCP table for their computers.  Some are only a day apart, but they are using the same MAC address.
warewolsAsked:
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mmarx82Commented:
I can't say for sure for the first part, I have seen the second part from one of our users using a hub and having 2 cables from the hub plugged into the switch (causing a loop). So I would check for any hubs or mini switches that are connected that way.
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warewolsAuthor Commented:
I have checked the whole area and cannot find anything plugged into the network other than the computers that I expected.  I am still searching though.
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sidetrackedCommented:
what does the core switch logs say?

if u are infact having a loop issue, check both switches cpu history "show processes cpu hist"

this might narrow down what u are looking for. you could also check for FCS errors on the ports both on coreswitch and on the edge switch, using the command "show tech | inc FCS"

if u have any FCS errors on the ports then your problem could be as simple as a speed/duplex missmatch, this can occur if u have autonegotiation enabled on the ports or if u have auto on one end and fixed value on the other
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warewolsAuthor Commented:
The history does not seem out of the ordinary for either switch...  Nothing above 30% utilization.  Also, I got nothing on the screen when I ran the show tech | inc FCS.
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sidetrackedCommented:
the logs doesn't date back that far, u have to check the cpu history within the next couple of hours from the incident.

try the "show tech" command and try to find the info regarding FCS errors, FCS=frame check sequence

FCS is often the easiest way to find mismatching link layer issues
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