Maybe the reader spits out more than one key per vvvv-frame.
Try the Buffered Keyboard Output pin on Keyboard (System Global Legacy) – you can copy the node from inside the new Keyboard (System Global) module – together with Tokenizer (String). Also check if the firmware of your reader allows to set some kind of end-of-line character that can be used as Separator on the tokenizer.
since beta30 contribution)-retrieves-the-keyboard-state-at-node-evaluation.-for-details-see-update-to-mouse-keyboard-nodes.-that-also-means-that-it-will-miss-certain-keystrokes.-the-old-node-(pre-beta30)-installed-a-system-wide-hook-(see-msdn),-which-was-responsible-for-some-nasty-UI-freezes-and-application-crashes.-so-we-decided-to-get-rid-of-it.-if-you-can’t-live-without-that-feature-have-a-look-at-the-((contribution:global-keyhook) posted by @herbst in the above mention blog post. it works in the same way as the old one.