The only number that I found that might be the number was 90260227. I found this on my invoice. Is there any way to confirm that this is indeed my serial number?

No, that doesn't look like a valid serial number, unless they've changed the scheme. Try going to the About menu on the player (it's an item in the main menu), then let it scroll down a bit - the serial number should be in there.

If you find it, please consider posting it here. It encodes the month and year when your player was manufactured plus a 'sequence number' - 1 for the first player, 2 for the second, and so on. We used to be able to tell from that number how many players were sold to date. Now this is no longer possible since there are multiple distribution channels but it still might give us some idea.

Borislav