No media uploading-error message

Hi,
I cannot upload to the Media Library. I can not add media through the add media page – nothing appears on that add media panel. If I use the ‘upload files’ tab, it appears as if to upload and then comes back with an error and nothing appears – but when you then check in the library, the media has been uploaded. But still unable to attach the media.

Using the latest wp and avenue theme. Gone through the process posted a year ago, but do not know where to look. I thought that with the upgrades bugs are fixed for things to work better. No techie skill, so if anyone is out there who can help, please, step by step is the key.

Thanks All