I had no problems uploading the image. Just remember that uploading an image of that size might take a bit of time (several minutes possibly) to upload. It's currently on your Gallery in the Main Gallery.
I also have a number of suggestions for your site, if you don't mind my advice:
1) That Logo is HUGE. It takes up the space of the whole website. I think it'd probably be better to move the current logo to a splash page of some sort. Remember, though, the splash needs to be HTML that is uploaded, not an image. In any case, having a logo of that size makes your site extremely difficult to navigate.
2) You have the custom menu created for the "Group Calendar" mod. I storngly advise moving that from a "Custom Menu" to a "Static Menu Item". The Static Menu items are much more tailored to large chunks of text such as you have included.
