You have OAS GUI set to display Warning messages in line24, but you want to display one Warning message in the big dialogue box, how can you do that?

This can be done by temporarily changing the PRGUI values for the Warning messages:
bulletFind your default PCGUISID, setting.  In model this is "DEFAULTS"
bulletCopy DEFAULTS into a new entry, say for example "WARNDIAG"
bulletChange the Warning message setting to "Y" (PCGUIDBW)
bullet 
bulletWhere you want the Warning Message to be a dialogue box stack $T=TNWARNON (OUTLINED BELOW)
bulletAfter your Warning Message occurs need to quickly the Warning back to a Line24 message, stack $T=TNWARNOF (OUTLINED BELOW)

That should about do it!
 

$T=TNWARNON
"%GECNGHX"='CHANGE GUI SETTINGS'
"PCGUISID"='WARNDIAG'
"%GURUNNG"='Y'
$PE=PCGUISID
$T=GUDTGUI1
 

$T=TNWARNOF
"%GECNGHX"='CHANGE GUI SETTINGS'
"PCGUISID"='DEFAULTS'
"%GURUNNG"='Y'
$PE=PCGUISID
$T=GUDTGUI1