I've tested it with IE 8/9 and it does work. But sometimes there is a communications glitch with the host servers. They can get temporarily over loaded, or go down for maintenance, which can cause the app to stall on "Preview". I've had this happened when using IMGUR's own website. In which case, you may need to close and restart the browser. Then reload the website app which appears to correct the issue.
In any case, Firefox does seem to have the fewest issues.