Possibly your IP was used by another person. Or you logged in-Searched within that time period which also triggers it.
If it doesn't occur too often,Just wait for 360 Seconds and see if it went through.

You might get more attention in the currency exchange sub-forum. Don't expect any good deals (or perhaps any deals) for PayPal though specially with a brand new account but some people might take dwolla.

IMHO it's not worth it anymore to mine btc with small miners, even with the current gigantic price jumps of btc's. You would only make ROI and a very small profit in a best case scenario.
On the other hand some alt currencies might be profitable specially low Hashes ones. And if they are listed on cryptsy/bter it might worth it.