Logo issues.
I see a broken image link at
http://www.organicchurchcommunity.c...mpromp2logoflexphotos.png
Is this a logo you edited in yourself? If so there is no image at this URL and the site is looking for it.
Normally all you have to do is change the image at templates/jj_flex_photos/images/branding-logo-red.jpg, and of course one for each color.
Custom Login.
Mambo development has slowed to a death crawl over the past few years. I cannot tell what version of Mambo you are using but I would think this might be your issue. If you see in the error it says josspoofvalue, and jos=Joomla. I would suggest giving Joomla a try and see if that helps a lot of the little quirks. On the up side you will have far more options when it comes to extensions and better security overall as Joomla is more actively being developed.
Hope that helps.