Thanks for your reply, I had figured it out after getting in touch with rebgui's developer who pointed me to the rebgui function library.
The example you refered to is actually a VIEW routine, and does not run under REBGUI, and took a small amount of conversion.

My revised example does run under Rebgui and used both the VIEW (show) & rebgui (set-text) style of displaying a fields value. Under rebgui you must make sure you use COPY to ensure your source data is not nulled.
Its a pity thot there dos not seem to be any complete small example program(s) showing this type of
problem. Plenty of code 'snippets' that assune you already understand the REBOL/VIEW context.
=========================
REBOL []
do %rebgui.r
display "test" [
f-name: field 20x8 font [ size: 18 color: black shadow: none ]
button "Set to Ann" 20 [
f-name/text: copy "Ann"
set-text f-name copy f-name/text ; REBGUI code
]
button "Set to Bob" 20 [
f-name/text: copy "Bob"
show f-name ; VIEW code
]
]
do-events
=====================