The error message says it all:Operand data type varchar is invalid for subtract operator

Variance = '$ ' + REVERSE(SUBSTRING(REVERSE(CONVERT(VARCHAR,cast(round(isnull(sum(Current_Tear),0),0)as money),1)),4,255)) - <<<<<< This is your subtract operator

'$ ' + REVERSE(SUBSTRING(REVERSE(CONVERT(VARCHAR,cast(round(isnull(sum(Previous_Year),0),0)as money),1)),4,255))

If you want to concatenate the "-" sign use this:

Variance = '$ ' + REVERSE(SUBSTRING(REVERSE(CONVERT(VARCHAR,cast(round(isnull(sum(Current_Tear),0),0)as money),1)),4,255)) + '-' +

'$ ' + REVERSE(SUBSTRING(REVERSE(CONVERT(VARCHAR,cast(round(isnull(sum(Previous_Year),0),0)as money),1)),4,255))

Otherwise, I have no idea what you're trying to do.