Why does this generate an error?

[Mark Swindell]

The following script is in a field, originalText.  It generates an  
error, yet at the same time it functions and puts the htmlText of the  
lines of field originalText into the messageBox.  Why does it  
generate an error  as it functions?
Thanks
Mark

on mouseMove
   global gMyLine
   put the mouseline into gMyLine
   put "the htmlText of " before gMyLine
   put value(gMyline)
end mouseMove

executing at 11:04:19 AM
Type    value: error executing expression
Object    OriginalText
Line    put value(gMyline)
Hint    the htmlText of