I see... Actually you will get this error so long as you aint using PHP 5.3.9 or above. There's a simple way of fixing the error, this support ticket should explain everything clear enough:
http://www.mysidiaadoptables.com/for...php?issueid=19
Note the reason why I asked you whether you were using PHP 5.3 is that the simple fix only works for users running PHP 5.3+. If you have PHP 5.2, you will eventually get into other issues that are difficult to resolve.