eBay seem to be really tuffing up on this :

Sellers are considered to have a limited selling history and therefore subject to holding of funds until ALL three conditions are met:

• It's been more than 90 days since your first successful sale
• You have more than 25 sales transactions
• You have more than $250 in total sales

But as padi said, I would contact eBay CS and see if they can lift the restriction.