Unable to write new post

For the last couple of days i’ve been having a problem, on + off, when i try to write a new post on my blog

https://www.scamemail.co.uk

i can write the title with no probs, but it won’t let me write the ‘body’ of the post.

theres a message on the bottom toolbar saying ‘Error on page’ (like i didn’t know!)

is this a problem with all wordpress at the moment?

a problem with the theme?

a problem on my pc?

can i fix it, or wait for it to go away?

any suggestions? (please make them ‘idiot-proof’ as i am not a techie or a programmer!)

thanks
kathryn