Most likely, it sounds like a spyware program has found its way onto your computer.  The removal of these programs is known to fix this problem.

In general, this is how spyware programs work: as you browse the web, the spyware turns random words into links.  These links then drive traffic to sites that pay the spyware company money.  The addition of these unsolicited links and extra html prevents your entry from being submitted, giving you your error.  Please note that a spyware program functions only on the user's computer and can not be installed on Xanga itself.  To ensure you do not have spyware on your computer, here are two programs that have been recommended for the problem: