Right, quotes are needed, but it's better to get in the habit of using single quotes (') for Kix, since the shell often requires double-quotes.
 Code:
shell '%systemdrive%\XXX\exprogs\runasspc.exe /cryptfile:"%systemdrive%\XXX\crypts\localadmin.spc" /quiet'
The double quotes in this example may not be necessary in your case, but illustrate embedding strings with double-quotes inside the Shell argument that is wrapped in single quotes.

Glenn
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Actually I am a Rocket Scientist! \:D