Oops that wasn't found when trying to update a static page

One of my pages needs additional content. I have a few paras in a word doc. I cut and paste it into the box ‘paste from word’ and then update and each time I put this specific set of paragraphs in, I get the Oops that wasn’t found message. I can paste completely different text in to that page and it accepts it. I have pasted the same text into another website.. and it was accepted. I have started a new page and used the same text and it will not accept it. I have checked any formatting in the text, tried to paste it as plain text.. no luck.
A friend tried it on his computer.. same problem. I have used different browser.. same problem.
I can’t even paste one paragraph of the offending text into the page. Has anyone ever come across this? it is very strange!