I am pretty sure you did something wrong,
you should not use that way on Sysinternals_Suite anyway, I wrote above for your standalone plugin following the way you suggest ...
personally, better not to use [Variables] for %PluginArch% .....
anyway,
On current
"Sysinternals Process Monitor"
and
"Sysinternals Suite"
plugins change this section:
[Add_fltmgr]
//to run procmon.exe on hostx64 both fltlib.dll required...
// Thanks, dera!
Require_File,drivers\fltmgr.sys
If,Not,ExistFile,%target_win%\fltlib.dll,Require_FileQ,fltlib.dll
//-
If,Not,%SourceArch%,Equal,x86,Begin
If,%TargetWOW64%,Equal,x86,Begin
Set,%PluginArch%,x86
Require_FileQ,fltlib.dll
Set,%PluginArch%,""
End
End
//-
If,%CoreType%,Equal,NT5X,Run,%ScriptFile%,Add_fltmgr_NT5X
Let us know it is all ok now