DELL PE T110 - two mac addresses on switch

[siki85]

Hi mates,

I have a problem with a PE T110, which has a server application to monitor snmp traps from remote equipments.

The server was working well, but recently it began to show network losses (icmp) and equipments started to lose registration with server.

The IT guys sent to me a snapshot of the show arp from a cisco switch
jf1-dis-2#show ip arp | include Vlan999
10.15.0.1 0 0026.b97e.37c7 ARPA Vlan999
10.15.0.1 0 0026.b97e.37c8 ARPA Vlan999

as you can see, the correct MAC would be 0026.b97e.37c7 but there is also a similar MAC with the same IP.
We tried to change the IP on the NIC, but the arp then shows this
jf1-dis-2#show ip arp | include Vlan999
10.15.5.1 0 0026.b97e.37c7 ARPA Vlan999
10.15.0.1 0 0026.b97e.37c8 ARPA Vlan999
and the problem still is there....

What could be causing this behavior ?
The server has only 1 NIC.

Any help would be appreciated....