Raymond, 

No, when I get this error no messages appear on the screen. 

You noted that in your company "some analyst tries to place an image in an entry the metadata stops to appear"

Is the issue user specific? If another windows users goes to the same machine, reboots it and logs in with their account (not the original user and one who does not have this issue), does the issue occur?

Is the issue document specific? For the same user, same machine, does the issue occur on all documents or only one or a few documents?

Is the issue machine specific?  If the same user goes to another machine, logs into windows with their own account and tries Web Access there, do they get the same behavior (i.e. issue follows them to another machine)?

What do you mean by the metadata stops appearing? Are the fields shown, but blank? Is the metadata pane open, but no fields are shown? Is the pane gone?

This sounds like it should be looked into as a support case. It's not something I've encountered as a general issue.