It all depends on the ATM machine that you want to dispense cash from. Usually, not all ATM machines supports all ATM cards. It is possible that the ATM machine you tried using is not compatible with the Sears Card. So I would suggest you try other machines as you might find one that will be compatible with the card. Make sure you use a machine that "Master Card" is paste on.
Also, network problem could cause a problem like this. If the Sears network service of the or the network service of the ATM machine you used is bad, it won't dispense cash. In this case, you will have to be patient for a while then try again later.
If none of the above seems to be the cause of the problem, then the best thing to do is to contact Sears. Sears will certainly point you to the right direction as to getting cash from your Sears Card. No one can give you a better information on your card that Sears.
To contact Sears, click here; http://www.citibank.com/us/cards/srs/contact_us.jsp
Call the phone number on the link.
Let me know if you need any more information.