Sparklz has good advice. Those blocks are very important to protect yourself and other buyers in the future who have their blocks in place.

Just aside - I have had very little trouble with e-cheques of the hundreds I have received only 2 have bounced - one buyer ended up with a strike the other was immensely appologetic, payed a direct deposit and has purchasedt from me again with no trouble.

It is very annoying though, hope it works out for you and I hope you get lots and lots of paying buyers soon!