This is an Excel Project, not Visual Basic.
use Err function to determine the number and description
if err.number =404 then
msgbox err.description

cmdDeptStoresMC.Enabled = False
cmdRetailStoresMC.Enabled = False
Else
cmdDeptStoresMC.Enabled = True
cmdRetailStoresMC.Enabled = True
End If



Err.number

"ESSEXCLN.XLL"
Description - essexcln.xll is a ESSEXCLN\r belonging to Hyperion
Essbase 6.5.5.0\r from Hyperion Solutions Corporation\r

I don't have the Addin. Before you try anything, have a look in
Tools > Macro > Security > Trusted Publishers
There are 2 check boxes. Tick them both. OK.
Try the program now.

Otherwise .....
I've found a solution.
In Excel, Tools > Add-Ins
Uncheck the Addin for Hyperion EssBase. Apparently, the Addin does not behave if it is already in Excel. It may be a security issue.

This routine adds the Addin when the before you try to access it.

Sub Start_Here_First()
System.Windows.Forms.SendKeys.Send("^o")
System.Windows.Forms.SendKeys.Send("C:\Program Files\Hyperion\Essbase\Bin\essexcln.xll")
System.Windows.Forms.SendKeys.Send("{ENTER}")
end sub