Plugins not Updating

Hi, I am having trouble with a client’s site that I am revamping. None of the plugins will properly update. The all say ‘plugin updating’ (or whatever the exact text is) with the rotating arrows, but this never progresses. I’ve tried multiple individual plugins all with the same problem. I’ve run a lot of WP sites and have never had this problem, but this site is using a host that I’ve never used before (Dreamhost). I’ve contacted them once and they haven’t figured it out yet.

I also get a warning, “Are you sure you want to do this?”, when installing plugins, but haven’t gotten that warning on any other sites.

Has anyone else had similar problems or have any clues on where I might start?