I also experienced the same problem, but my problem was resolved by running the following code before proc panel program:
*Eliminate missing variables;
DATA WANT;
SET combine2;
IF win = . THEN DELETE;
IF loss = . THEN DELETE;
IF fb = . THEN DELETE;
IF bjk = . THEN DELETE;
IF gs = . THEN DELETE;
IF national = . THEN DELETE;
IF fbwin = . THEN DELETE;
bjkwin= . THEN DELETE;
gswin= . THEN DELETE;
fbloss= . THEN DELETE;
bjkloss= . THEN DELETE;
gsloss= . THEN DELETE;
IF GVKEY = . THEN DELETE;
IF datadate = . THEN DELETE;
RUN;
*Ensure each gvkey must have at least 2 observations;
proc sql;
create table want as
select * from want
group by GVKEY having count(*)>= 2;
quit;
*sort the data according to gvkey and datadate;
proc sort data=want;
by gvkey datadate;
run;
I hope this codes are useful.
Good luck.
Regards,
MSPAK