You cannot just mention "Select all" you need to mention the RO property as well in order to identify the "Select All" option from the weblist or webtable.
1) are you using DP? or you are usnig record and playback?
Because in both the instances, the parametrization will be different.
If you want to create the object from the webtable you have to write the next line:
set objName=Browser("bla").Page("bla").WebTable("blabl a")
if the webtable is in iFrame I supose you have to write the next:
set objName=Browser("bla").Page("bla").Frame("bla?").o bject.WebTable(-here you have to write not OR name but some set of identificators using descriptive programming-). "supose" means I haven't faced such situation. Maybe instead of WebTable you'll need to write WebElement. You have to experiment with this.
If it's not hard could you tell us result?