Use & in your calc rather than + to concatenate the two fields.
I created a list of FMP links, you may find some useful.
Formatting Numbers in a Text Calculation Field
I had to un-check the "Do not replace existing value of field (if any)" box and my forumla now looks like this:
LakeName & " " & MonthName ( DateStudied ) & " " & Round (Year ( DateStudied ); 0)