String Concatenation fails CR10

Hi,

I'm trying to concatenate two (same)strings in a formula with different formats,some time it works, sometimes its empty in the production environment which is really bothering.Could you please help in fixing this issue.

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ToWords ({tblTableName.NumberField},0 ) & " (" & ToText ({tblTableName.NumberField}, 0) & ")"

Above is the piece of code used in CR10(Crystal syntax).Also I want to know is there any difference between '&' and '+' in using for concatenation.