AUTOCAD 2013 Error: _sheetset unknown command "sheet set"

PROBLEMS:
Some buttons would not work.

BUTTONS:
My personal buttons work, but some AutoCAD's default buttons would not work and give me the error ´ _sheetset unknown command "sheet set" ".

FUNCTIONAL BUTTONS:
New, Save, Open, & Print
NON FUNCTIONAL BUTTONS (Both in my workspace and AutoCAD's workspace):
SheetSet, DesignCenter, Properties, & Tool Palettes Window.

CUI:
Created (New) my personal CUI in the CUSTOMIZE tab.
Created (New) my personal CUI in the TRANSFER tab.
In TRANSFER tab, transferred my personal toolbars to ACAD.CUIX.

WORKSPACES:
Saves As my own workspace.
Reverted to the AUTOCAD CLASSIC & DRAFTING AND ANNOTATION.

MENU:
From the AutoCAD's default menu, enabled the STANDARD toolbar.

AUGI FORUM:
I searched for " _sheetset unknown command "sheet set" ", not post to read.

FOOTNOTE:
All buttons work if I reset AutoCAD. I have done this more than ten times and I am frustrated by now in recreating menus and toolbars and links. I hope I have given enough information to get help.

From the sound of it, " _sheetset unknown command "sheet set" " isn't actually your problem just a sympton of it.
The problem seems to be the interaction between your input device/buttons and the menu system/CUIx.
What is your input device?

"Input device"?
OK, I use both USB Dell mouse and keyboard.

So, by "buttons" you mean toolbar buttons? Not physical buttons?

It sounds like (some of) your .arx routines are not loading.
Type APPLOAD to see which routines are loaded.
Toolpalettes loads acTp.arx. DesignCentre loads a range of .arx routines whose names start with acdc...