Voicemail from Snom300

When I dial VM from a Snom300, its prompts me for my password, as im typing in my password, Asterisk CLI is giving me the following error:

[2013-09-10 14:00:15] NOTICE[16823][C-0000000e]: res_rtp_asterisk.c:3696 ast_rtp_read: Unknown RTP codec 1 received from ‘’.

Then it proceeds to say login incorrect, this does not happen with other phones. I tried to look up what RTP codec 1 was, and I could not find any useful information about it.

Please help!