I had plg_easyflashuploader_v3_0_fixed installed but wasn’t using it. Then without uninstalling this version I installed plg_easyflashuploader_v3_1 over the top, no error messages, all looked good but it wouldn’t upload. After uninstalling and reinstalling v3_1 file uploads worked fine.
Installing over the top of a previous version was not causing the problem as I went through this again installing over the top of v3_0 to V3_1 but the file upload worked fine this time.
It may be worthwhile if having an upload problem to uninstall then reinstall, always think about backing up before you make changes to your site…