Thanks for advising Dr. Tam, The series of errors I've encountered and their solutions
1.
error task 1 failed - "subscript out of bounds" the issue is the give file should meet the conditions of column (even they seem similar file but there would be different columns).and whenever we give a Filetype we should also include it's function if left empty the following result "Cannot open the file connection"
2. the observed flow file should be only named "obs_var_1" and the length of the fil should be exactly same as the simulation period you mention in RSWAT.