I've been having problems, too - but it's not all bad news
Just because you get an error message in the uploader, doesn't mean your image hasn't uploaded - error messages are sometimes... well... erroneous. Open the partly uploaded gallery in a new tab and have a look before you panic and refresh that tab any time you get an error - you may be pleasantly surprised!
Vary your file sizes. If you try to cram endless 9+Mb files into your gallery, one after the other, then that creates a kind of 'logjam' effect which is almost certain to produce error messages. Intersperse large files with a few smaller ones of (say) no more than 6-7Mb, especially in the first five uploads. This will start to build up an 'offset' in the uploads, which become staggered as a result, thus avoiding a logjam.
Hope that helps.