Well I found the solution

Here it is in case anyone else comes looking. I thought the error was that it couldn't find the file newstring.mcc. It suddenly occurred to me that maybe it can't find the drawer it wants to copy it to. So here's what I did:
Add the following to S:user-startup
Assign MUI: SYS:Classes/MUI
Assign LIBS: MUI:LIBS ADDThen create the drawers SYS:Classes/MUI and SYS:Classes/MUI/LIBS. Then install iBrowse and it works

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moto