When you bought the property, your solicitor clearly covered your interests by ensuring an indemnity policy was purchased. Often the way is to force the seller to pay for it - but it isn't too much money - perhaps a couple of hundred pounds.
When you decided to sell, the most helpful thing would have been to have remembered this, and mentioned it to the solicitor acting for your sale. Nevertheless, in getting hold of your title, your solicitor should have discovered it and at least mentioned it to you as something any buyer of your property would find - in much the some way as your original solicitor did when you were the buyer.
As to your claim that it prevents you exchanging, I just don't get it - these policies are normally easy to fix up - could be done in a day over fax machine with one of the big insurers - Norwich Union is but one company that does these policies.
As to your solicitor giving you 'bad' advice, I'm not sure I agree - are you suggesting he should have been shouting from the rooftops at any prospective buyer 'this property has a defective title and is going to need an indemnity policy' - that's what the buyer solicitor is for. You new buyer's solicitor should have found this out when examining the title.
But as I said above, sorting it takes little time - but expect the buyer to want you to pay for it.