Windows Media Player problem

[Sophy]

I have a fairly new Dell XPS410 with Vista Home Premium. I have Windows Media Player 11. I received a WMA attachment from a family member and it won't play. The message I get is:

Windows Media Player cannot play the file. The Player might not support the file type or might not support the codec that was used to compress the file.

I don't even know what is meant by codec. Can anyone help me? I wrote to Microsoft but no answer.

The same family member also sent me a WMV file and it wouldn't play either; then after about 6 attempts it finally did and I didn't change anything or do anything.

Thank you,

Nikilet