It’s the same cause as for all recent problems - Bitcoin Core is causing problems and when Counterparty interacts with it, it reports it’s not ready or similar errors.
It is partially because of suspected bugs in Bitcoin Core 0.10.x and probably the recent “stress tests” that people have been running on bitcoin mainnet are causing additional problems.
There is no solution at the moment. A temporary workaround is to periodically restart Bitcoin server (which then causes short downtime, but not restarting it after a while causes service errors).
Please try https://counterwallet.coindaddy.io (you may notice the same issue there, although probably not at the very same time) or retry periodically on https://counterwallet.io.
Edit: there are “stress tests” or attacks on Bitcoin going on these days, see the charts at http://cointelegraph.com/news/114782/bitcoin-transactions-surge-to-record-highs-amid-greece-crisis or https://blockchain.info/charts/n-transactions?showDataPoints=true×pan=30days&show_header=true&daysAverageString=1&scale=0&address=, which makes above mentioned bitcoin daemon problems even more pronounced.