I am trying to run a code which is written in FORTRAN and I get this error:

Linking...
GRAV_EST.OBJ : error LNK2001: unresolved external symbol _TLINEX@64
GRAV_EST.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.
GRAV_EST.exe - 2 error(s), 0 warning(s)

How can I resolve this problem? The code isn't mine and I am not that much familiar with FORTRAN. Thank you for your help.