Were you able to place any bids on an item after the first purchase?
If the seller is brand new, they may have gone through the seller account settings and implemented a few auto-blocks, maybe (or maybe not) understanding exactly what they will do. One of those auto-blocks will prevent members from bidding on or purchasing more than a set number of items in a certain period. The general purpose of this block is to try and stop malicious bidding / buying, or possibly fraudulent behaviour (if, for example, someone was selling very expensive items that people typically only buy one of, eg a big screen TV, they might want to stop people from buying a bunch at once and exposing themselves to a higher chance of fraud involving heaps of cash), but in light of all the upcoming changes on eBay / PayPal, I wouldn't be surprised if there's quite a number of sellers with increasing paranoia about all kinds of issues and will just take every measure available no matter what.
Anyway, the point is, they may have not decided to block you personally, just implemented a global block when they set up their seller account. There is also an auto-setting to prevent blocked bidders from sending messages, but you should still be able to contact them through your current purchase.
If, on the other hand, you were able to bid on an additional item and then found you weren't able to bid on it any further, that would tend to indicate a conscious choice on behalf of the seller. Why is anyone's guess, really, but for the time being it would just be a matter of waiting to see if you get the orignal item, and all is as described etc.
