救助：SAS宏编程问题

%MACRO TEST;
DATA ECSUBSET;
  SET ESTCOV(WHERE=(EFFECT="&VCENTVAL" AND PARAMETER=ROWNAME));
  NOBS+1;
  CALL SYMPUT('NOBS',NOBS);
  RUN;
  %PUT NOBS= &NOBS;

  %LET KEEPLST=;
  DATA _NULL_;
  %DO EC=1 %TO &NOBS;
    J=&EC;
    SET ECSUBSET POINT=J;
    CALL SYMPUT("VAR&EC",PARAMETER);
  %END;
  STOP;
  RUN;

  %DO EC=1 %TO &NOBS ;
    %LET KEEPLST=&KEEPLST &&VAR&EC;
  %END;
  %PUT KEEPLST= &KEEPLST;

  DATA VCMATRIX(DROP=EFFECT PARAMETER ROWNAME);
  SET ESTCOV(WHERE=(EFFECT="&VCENTVAL" AND PARAMETER=ROWNAME) KEEP=EFFECT PARAMETER ROWNAME &KEEPLST);
  RUN;

  PROC DATASETS LIBRARY=WORK MEMTYPE=DATA;
  DELETE PARM RT_EST_TEMP ADDPRM COVPARM ESTCOV ECSUBSET;
  QUIT;
  RUN;
%MEND TEST;

报错如下：
ERROR: %EVAL function has no expression to evaluate, or %IF statement has no condition.
ERROR: The %TO value of the %DO EC loop is invalid.
ERROR: The macro READCOV_T will stop executing