Most likely name of action associated with those files is not 'Open'.
Try

lnRetVal = Shellexecute(0,"",lcFile,"","",3)

>Have been using ShellExecute with Pdf file for a while without any issue
>Try to use now with .jpg and .tif and am getting back a 'File Not associated'
>
>However, If I double click the same file, Paint opens them up both no problem. I can also see in Control Panel..Default Programs that these two types of file seem to be correctly associated
>
>Should ShellExecute work with all associated files or do I need to change something
>
>Command I am using :lnRetVal = Shellexecute(0,"Open",lcFile,"","",3)
>
>Tia
>Gerard