Most probably, your eBay account has reached the limits or the eBay system incorrectly decide that your account exceeded the limits. Please find more info about eBay limits here: http://pages.ebay.com/help/sell/sellinglimits.html
The first error: "The item cannot be listed or modified. The title or description may contain improper words, or the listing or seller may be in violation of eBay policy. ", you should ignore, as eBay send this confusing error each time with the second one, which is the real reason why items cannot be listed.
Note: All errors are returned by eBay, M2E Pro just displays them.