Problem putting some new Items.

I notices several times when i need to put a new Item, the site give me an error page "is not a valid url"

Is there a solution for this?

Post the urls here and I will investigate

Thank you Tom.

Here are some examples I have:

twokinds.keenspot.com/ and
www.sandraandwoo.com/

there are more, but I don't remember anymore their links.