maximum total uploads

I need to upload some files to my site that are about 200kb. Well below my file size restriction in php.ini which is 50MB. But I keep getting "http error"

I did some digging and found this

http://www.charlestonsw.com/wordpress-max-file-size-reached-check-wpmu-limits/

which suggests that WPMU might be enforcing it's own file size limits and blocking the upload. The site is getting close to over 500MB in size so it could be breaching the 'maximum total uploads' setting. My question is where is this setting and how do I change it?