Adding comma to string

Hey all,
I need a little help adding commas to this string. When I run this code below I get the result, A-(BCD)-(BCDEF). What i want is A-(B,C,D)-(B,C,D,E,F). I tried adding a join to it but keep getting a type mismatch error. Any help would be appreciated.

thanks
jeremy

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Something like this, im not in excel at the mo so havent tested.