Total Posts: 12
This message can mean many things like database issues, resource shortage or incompatibility of themes and extensions ( if theme is the case, try switching to the previous one)
First, check your error logs in var/report - maybe it will give you some clue.
Another variant is to clear cache and disable compilation.
Also, you may try disabling additional modules and flushing the cache.
If the problems continue, you may just use a monitoring service (I am using shopping cart diagnostics) to nail down the problem.