Base URL not reading correctly with relative paths

With standard Joomla SEF on (all three options), all is working well.  When I activate SEF Advance, the base site URL is not reading correctly, thus all of my image paths are broken.  You can see a sample here:

beta.cheresources.com/articles/sizing-of...-in-acid-plants.html

I'm using title alias with lower case, include section is yes, include category and unique id are no.

You can see that the first image link is:
beta.cheresources.com/articles/images/ar...dpacktower1print.gif

which is not correct.  It should be:
beta.cheresources.com/images/articles/th...dpacktower1print.gif

The section name is being carried over to the relative image URL.  If you look at the source code of the page, you'll see the correct, relative URL for the images. 

I need advice.

Thanks,
Chris

It was base href tag that was not inserted in head. It's now fixed in 1.5.6.

Thanks for the help Emir.  That problem is solved.  Next is probably easy:

I'd like to EXCLUDE the category and the section from my URL's (which will save me from having to do a lot of redirects).  But, I have an expandable menu (if you click on Articles on my test site at beta.cheresources.com ).  The sub-menu items include the section in them, thus they won't route if I turn section and category off.  I thought this would be a good place to use an alias, but I can't seem to get an alias of any kind to work properly.  Any further advice?

Thanks,
Chris

This sounds like an Itemid issue. Check the FAQ for this.
When I'm back I can take a deeper look.

OK, article and menu trash are empty.  Debugging is turned on.  Indeed, under the article sub-menu, all of the items are reading Itemid = 4 (which is the article section).  I've ready through the FAQ, but I still don't understand how to get these menu items to work correctly without showing section or category in the URL.  I guess I need a little more help.

I even tried making a new menu item under Articles with the same results.

Thanks,
Chris