Proc export does not work

When i execute the following code :
filename  tst  "c:\data\best.xlsx" ;
............................
code
............................
proc export data = number
     outfile = tst
     dbms = xlsx or excelcs replace ;
run ;

the result is no output file.

When i execute the following code :
............................
code
............................
proc export data = number
     outfile = "c:\data\best.xlsx"
     dbms = xlsx or excelcs replace ;
run ;

then everything works fine.

What i am doing wrong?

Tx