Windows 7 x64
Process Hacker 3.0.1118
If you try to delete an environmental variable for some process and this operation occurs to be unsuccessful no error message will be displayed.
To show an error message, just like what happens when you try to edit this variable instead of deleting it.
How to reproduce:
The simplest way is to create a new process with CREATE_SUSPENDED flag and try to delete some of its environmental variables in this suspended state.