IMCE File Browser Ajax Error

Every time a user tries to navigate the IMCE file browser or upload a file, they get an Ajax error. If they're lucky, they can see their initial folder but can't really do anything.

An AJAX HTTP error occurred.
HTTP Result Code: 500
Debugging information follows.
Path: /imce?jsop=upload&dir=sites/default/files/user_uploads
StatusText: Internal Server Error
ResponseText: {"data":{"added":null,"dirsize":"9.57 MB"},"messages":{"error":["The specified file \u003Cem class=\u0022placeholder\u0022\u003Esrsudirectorybycampus_1.pdf\u003C\/em\u003E could not be uploaded. \u003Cem class=\u0022placeholder\u0022\u003Esrsudirectorybycampus_1.pdf\u003C\/em\u003E is \u003Cem class=\u0022placeholder\u0022\u003E978.08 KB\u003C\/em\u003E which would exceed your directory quota. You are currently using \u003Cem class=\u0022placeholder\u0022\u003E9.57 MB\u003C\/em\u003E of \u003Cem class=\u0022placeholder\u0022\u003E2 MB\u003C\/em\u003E.","Upload failed."]}}

An AJAX HTTP error occurred.
HTTP Result Code: 500
Debugging information follows.
Path: /imce?jsop=navigate&dir=u238
StatusText: Internal Server Error
ResponseText: {"data":{"files":"\n\u003Ctable id=\u0022file-list\u0022 class=\u0022files\u0022\u003E\u003Ctbody\u003E\u003C\/tbody\u003E\u003C\/table\u003E","dirsize":"0 bytes","subdirectories":[],"perm":{"subnav":0,"browse":1,"upload":1,"thumb":1,"delete":1,"resize":1}},"messages":[]}