In certain cases, when the IP phone initially fails to resolve the Cisco Discovery Protocol, it can mistakenly try to use the native VLAN. If the Dynamic Host Configuration Protocol (DHCP) on the native VLAN answers, but does not provide a valid TFTP server, the application loader can fail.
perform these steps for resolve .
1.If a DHCP server is configured on the native VLAN, make sure that option 150 information points to a known and functioning Cisco CallManager system.
2. Make sure that the TFTP and DHCP options are configured properly.
If step 1 and step 2 do not help change the switchport from a trunk port to an access port, once the phone registers to the Cisco CallManager, change it back to trunk port.