Hi Ken,
I just found out that there is some problem using in JS (prototype) this line:
$get(this._Uploader).internalobject.insertBtn.style.display = "none";
Somehow the internalobject or insertBtn is null or empty so there seems to be two dots ".." generated on js code.
Replacing that line with this one solved the problem:
$get(this._SelectFilesButton).style.display = "none";
I'm using external button for this to work. but so far seems ok. Thanks for your help.