iPod Credit balance out of date?

I've been getting this error message on my iTunes consistently.

I've been buying gift cards and currently have a gift card balance of $3.52 (Canadian). I also have a credit card on file as backup.

Whenever I try to purchase a 'free' song, a 99cent song, or a full album, it gives me the above error message.

I've restarted iTunes, restarted my computer, and it still gives me this error. I can't even buy anything! (or download singles of te week)

any suggestions?

Thanks - I've taken a look at that link, and have seen similar discussions on apple help discussion foruns previous to posting here, and there never seems to be a definite solution other than 'spend more money first'. My problem is that I've tried free, 99cent, and also full albums, and no matter what I buy I get this error message. In many of the discussions I have read, the individuals ended up 'purchasing' every item they clicked on, but they never did download. I don't want to keep clicking on everything and end up in a similar situation of being charged for a whole bunch of stuff I clicked on.

I've also sent a note to iTunes tech support, but they said there is a huge volume of queries now and responses could be quite significantly delayed. That's why I came here.

I also have another gift card I have not yet redeemed until this problem is resolved.