Error message

[sweaver99]

I'm getting a fairly constant Error Message, but only when I play one of my characters, not any of the others. It says;

Interface/FrameXML/UIDropDownMenu.lua
Line 149
Count 6
Error: attempt to concatenate global
'UIDROPDOWNMENU_OPEN_MENU' (a nil value)

Anybody know how I can fix this? Or at least make it go away?

Thanks in advance.