SQL SERVER Error: "A SELECT statement that assigns a value to a variable must not be combined with data-retrieval operations."

I don't what your trying to do in this query. As far the error is concerned this could be solution. I am sure but give a try hope it works :). Split it into two different queries.

SELECT @CRIME_DETAIL_1=count(*) 
FROM t_crime_detail
  where RECORD_SYNC_FROM='PS'and PS_CD=@PS_CD
  and CONVERT(date, RECORD_CREATED_ON)=@REG_DT;

SELECT ( SELECT t_fir_registration.PS_CD FROM t_crime_detail INNER JOIN t_fir_registration ON t_crime_detail.FIR_REG_NUM=t_fir_registration.FIR_REG_NUM) AS PS_CD 
FROM t_crime_detail
 
  where RECORD_SYNC_FROM='PS'and PS_CD=@PS_CD
  and CONVERT(date, RECORD_CREATED_ON)=@REG_DT;