Invalid XHTML response for an AJAX request.

What is the best way to handle this error: (Invalid XHTML response for an AJAX request.)

I have values within my drop down which contain the chars that cause this error.  I have avoided this with '&' and replaced values with 'and' but can't really do the same for '<', '>'. etc?

I get around this by say using:

REPLACE([Measure], '<', '&lt;') [Measure]

but then I have to change this back in my SQL query also?  Is there a cleaner way to handle these chars?