Error when adding link to product/category description

[discountpoolspa]

Whenever I try to add a link or image to any product or category description (using the admin 'edit category' or 'edit product' function) I get a '500 - Internal server error' when I try to save it.
HTML formatting works perfectly in both cases, but if I have an image link or url link, it gives me this error.
Sample problem code:

Replacement Cartridges and Grids<br/>
Click <a href="http://www.unicelfilters.com/retailers/" target="_blank">HERE</a> For a helpful <a href="http://www.unicelfilters.com/retailers/" target="_blank">guide</a>.

<img src="http://website.com/image.jpg">

Any Ideas why?

[discountpoolspa]

No One has seen this before? No ideas?