I've seen this problem -- "Market is closed" -- from time-to-time and today I decided to contact my broker to see if they had an explanation. Here's the response:
Actually when liquidity becomes very thin and we are not receiving any quote/price ticks or market is not moving. Any pair will be greyed out and will not be tradable until the next quote/price tick is received. Liquidity becomes very thin usually at the end of the day.
Whether all brokers follow the same policy, I have no clue. But this explanation makes sense to me and I appreciated they were honest about it.
So, the bottom line, the MT4 error message is misleading. The market is not necessarily closed, but your broker has temporarily stopped trading a particular pair. I don't think there is anything evil going on, just that the broker is protecting themself.
As to what we can do -- I don't know. Perhaps Popov or one of the moderators has a suggestion. For now, I'm not going to worry about it and I'm certainly not going to change brokers.