The code seems to be fine. What are the types of columns docid,docno,cocode,reportid in the tmp_csrvpv?
Are you sure tha message doesn't say 'Cannot convert..."?

>create table #CursorRVPV
>(docid nvarchar(10) not null,docno char(20) not null,cocode nchar(10) not null,paidinvamt decimal(9,2) not null,paidbaseamt decimal(9,2) not null,reportid nvarchar(50) not null)
>
>INSERT INTO #CursorRVPV
>(docid,docno,cocode,paidinvamt,paidbaseamt,reportid)
>SELECT docid,docno,cocode,SUM(paidinvamt) as paidinvamt ,SUM(paidbaseamt) as paidbaseamt , reportid
>FROM tmp_csrvpv  GROUP BY docid,docno,cocode,reportid

>I got any error named" cannot equal to .... order"(<-- it is in chinese")
>What's wrong with my statement?