How to pass LOCALFILE to Library.nsh as a variable

[jsbach]

i wish to pass a dynamic foldername to upgrade all its DLLs/OCXs but i'm getting the error:
'!error: InstallLib 1: The library $5\$1 could not be found.
Error in macro InstallLib on macroline 89'.

Even tried to !define a custom var (i.e. var MyVar) and use it (with StrCpy $MyVar "c:\sourcedir": no way.
I've read almost all relevant posts in this forum but i must admit i can't still understand where the issue is: i would really appreciate just some hints.
Here below the abstract of the code i'm using.
Thanks in advance.

;test upgrade all dll in a given folder
!include Library.nsh
var ALREADY_INSTALLED
name "Get files test"
outfile "testgetfiles.exe"
InstallDir "$PROGRAMFILES\MyTest"

Section -DoIt
push "c:\sourcedir\winlib"
call GetFiles
SectionEnd

Function GetFiles
Exch $5
FindFirst $0 $1 "$5\*.*"
loop:
StrCmp $1 "" done
StrCmp $1 "." readnext
StrCmp $1 ".." readnext
ifFileExists "$5\$1" 0 readnext
StrCpy $ALREADY_INSTALLED 1
!insertmacro InstallLib REGDLL $ALREADY_INSTALLED REBOOT_NOTPROTECTED "$5\$1" "$SYSDIR\$1" "$SYSDIR"
readnext:
FindNext $0 $1
Goto loop
done:
FindClose $0
FunctionEnd