It's been a long while since my days with psexec... but looking through an old script I used(and ick did I have some bad coding habits back then), it appears the remote path needs to be a unc path not a local path.

I cobbled this code together from my script, and it is untested, but should show you enough of what I was doing.

 Code:
$remotesystemroot=readvalue("\\" + $remotepc + "\hkey_local_machine\software\microsoft\windows nt\currentversion\","systemroot")
$remotesystemroot=right($remotesystemroot,len($remotesystemroot)-3)
$remotedestdir="\\" + $remotepc + "\" + c$ +"\" + $remotesystemroot + "\system32"
shell $vncdir + "\psexec.exe" "\\" + $remotepc + " -i wscript " +  $remotedestdir + "\yesno.vbs"
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(... better days ahead)