Seeing as I've just had this problem randomly occur at my office on a coworkers computer, the Original poster @max_bellato has told you everything you need to know. The problem being that the default "copy and paste" whether it's used from a keyboard command or right click menu results in an ole object being pasted, something that should only happen when using the paste special command from what you yourself have said
. Reading your replies is frustrating because it was a simple question and you massively *complicated* it by refusing to listen since message 6 where the answer should have been "there are no settings for changing the default paste to or from special paste" or "I don't know".
As another user of Autocad since 98, I can say that the program occasionally causes random settings changes that weren't input by the user and thus aren't known by them to change it back. Whether it's a command without a prompt like this paste issue or a "lengthen" command that suddenly defaults to (D)elta instead of (T)otal, these are normal use issues, and while a screenshot may have been helpful to understand what should have already been understood, the condecension in the replies wasn't.