The plugin sounds like Scriptmaster from 360works.
It may be you don't have the full path. You also need the volume.
or you have missed out (relative path) file:$path or (fullpath) filemac:$path in the Import Path List
(I found out about both these issues through trial and error at first! )
The following works for me to get a fullpath
Set Variable [ $filePath; Value:SelectFile ]
Set Variable [ $Volume; Value:Get(SystemDrive) ]
Set Variable [ $fullPath; Value:Left ( $Volume ; Length ( $Volume ) -1 ) & $filePath ]
If [ $filePath= 0 ] //User cancelled
Exit Script [ ]
I am not sure where the plugin came from, but I do also have the 360 Works plugin.
Your solution works well and of course looks like it will be suited to both Windows and Mac runtimes.
A follow up. (after bug testing a solution for Windows)
The volume only needs to be appended to the Mac filepath returned by Scriptmaster to make a full path.
On Windows Scriptmaster already returns a full path. BUT it returns it in windows format
this will need to be converted to C:/folder/file for filemaker to use it.
Set Variable [ $FMfilePath; Value:Substitute ( $filePath ; Char ( 92 ); Char ( 47 ))]
"\" causes problems in the formula hence Char ( 92 )
If you use Scriptmaster to run other functions requiring a filepath, it should stay in Windows format