Running rebaseall on Cygwin

Try invoking ash by giving its full pathname. For example, if you installed Cygwin into C:\cygwin\, then you would type this into the Start/Run dialog box:

C:\cygwin\bin\ash.exe

This should start the ash shell, within which you can then invoke /bin/rebaseall.

If you are running Cygwin-X make sure the X is closed, not just the xterms.