You should be able to to just two fields:
concat( field1, field2 )
Maybe you forgot to delete the last comma when you deleted the third field. If the above doesn't work, just make the third field and empty string:
concat( field1, field2, "" )
However, the cool thing about concat is that it accepts (I think) an unlimited number of arguments, so the following will even work:
concat( "1", "2", "3", field75, field80, " Quote of the day", "etc.", "etc." )
Please don't get any brain on the carpet. :)
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Matt Faus
InfoPath Dev Texas
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge