I have set up a multisite and currently have 3 sites - the main site is complete and I am starting to build landing pages on the other 2. The media library works fine in the main site, however, in the 2nd and 3rd site the media grid just sits and spins and will not let me upload any images - I get an error. If I switch to media list mode i can upload via the browsers builtin uploader and see the images. I can not place the images on my pages or add a logo to the headers because they are accessed via the media grid & upload. I have tried looking at my permissions and they seem to be set correctly.
I have also noticed an error message that appears at the bottom of the dashboard on the 2nd and 3rd sites. It says "An internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, [no address given] and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log." I have contacted my hosting provider about the error but they can't find any errors for those sites.
I am at a loss as to how to fix the issue and I can't go any further in building without resolving.