The ISS Unix workstations are mostly Sun machines running the CDE (Common Desktop Environment) window system. The operation of CDE's graphical interface depends on certain settings which may be at variance with those required in a non-window interface.
Appropriate standard settings for CDE are arranged automatically. However, these can be altered to suit individual tastes by the use of the .dtprofile file. The first time you login via CDE, a standard .dtprofile file is created automatically in your home directory.
When you login via CDE, it is possible that .dtprofile will be executed instead of .login. However, apart from the special CDE settings, there will almost certainly be others you will require in all forms of Unix access. To avoid repeating these in .dtprofile, it is desirable to invoke .login as well when using CDE.
It is essential that your .login settings do not conflict with CDE's own requirements. The standard ISS .dtprofile file contains comments describing the rules for constructing an appropriate .login and explaining how to cause .login to be executed automatically.
If you have any problems concerning the execution (or not) of your .login file, one of the places to look is .dtprofile. If this file contains (at the end, probably) the line
DTSOURCEPROFILE=true
... then your .login is being executed. If DTSOURCEPROFILE is set to false, or the line is commented out (# as first character) then your .login is not being executed.