the first path of your xpath expression is invalid:
For complex xpath locators like the one you use here, I'd suggest using find, then this would look like that:
alternatively, you could chain multiple smaller expressions to create the one you want:
By the way, you don't always have to specify the full path to the child element you want, often it is sufficient to use expressions like //table[@id='myTable'] and SilkTest will match that against all children and return the first control matching the locator.
Hope this helps