It's often clearer to break up long command lines into bits.

You could try the multi-arg version of system, but I'm never quite sure what goes on under the covers and find myself guessing how to arrange for things to get interpolated and quoted correctly. DIY often seems easier to me.

Try:

system join ' ',
    'psexec.exe',
    '\\\\aisfs01.gcps.k12',
    '-u username',
    '-p password',
    qq[ "e:\\psoft\\batfls\\$product{commandstop}" ]
;
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