Automation error. Key not found.

[john.uhden]

After setting 'layers to the layers object, I stupidly assumed that (vla-item layers <name>) would return nil if the <name> layer didn't exist.

WRONG, you get the Automation error.

Simple fix...

(setq name "whatever")
(and
  (tblsearch "layer" name)
  (setq layobj (vla-item layers name))
  ;; continue
)

because (tblsearch) will return nil if the named layer does not exist, and will cease further evaluation within the (and ...).

Yes, you could use the catch-all approach instead.