我是试用从WRDS 上下载的SAS code做的动量策略，例子里的数据是从CRSP 上下载的美国股市1965-1989的数据（sas格式），用这个的时候，这组code运行的很好，结果也和例子一样，可是当我换了一组变量名称一样的excel格式的数据时，系统出现了好多错误，这是怎么回事啊？我在换数据的时候，名称都对应和例子里的一样！而且我sas9.1和8.2两个版本都试了，都是一样的结果！请教高手这是为什么？下面是错误的地方：
178  proc sql;
179      create table umd
180      as select distinct a.permno, a.date, exp(sum(log(1+b.ret))) - 1 as cum_return
181      from msex2 (keep=permno date) as a, msex2 as b
182      where a.permno=b.permno and 0<=intck('month', b.date, a.date)<&J
183    group by a.permno, a.date
184    having count(b.ret)=&J;
ERROR: Expression using addition (+) requires numeric types.
ERROR: Function INTCK requires a numeric expression as argument 2.
ERROR: Function INTCK requires a numeric expression as argument 3.
ERROR: Expression using less than or equal (<=) has components that are of different data types.
ERROR: Function INTCK requires a numeric expression as argument 2.
ERROR: Function INTCK requires a numeric expression as argument 3.
ERROR: Expression using less than  (<) has components that are of different data types.
185  quit;