Q:

Why do I get an 'SDK seems invalid' error when setting up my Project Interpreter in PyCharm? 

I try to set up project interpteter Python 3.5 in Pycharm and get an SDK error? 
Any solution to fix it? 

A:

did you move the whole project after you open it with pycharm? 
if so, just remove the .idea/* (run rm -r .idea under you project)
This problem is caused by: pycharm will create a .idea file under the project after the first time you import the project.  SO the path in there will remain the old one after you moved the project.  Thus the pycharm will keep trying to import 'old_path/venv/bin/activate' which is kept in .idea/*

A:

I just had this error and got around it, and long-story-short I think it may have had to do with my PATH / PY_HOME / PYTHONPATH environment variables pointing to a different version of Python.  Here's what I did:
Background:

In my case, I was trying to get a Python 2.7 venv running on a laptop where I'd previously been working with Python 3. 
I'm using Windows 7. 

Solution:

Hit the Windows key to pop up the Start menu. 
Type out 'path' and hit Enter. 
The 'Environment Variables' window should appear. 

There should be two sections of the window:

One should say, "User variables for your_user_name". 
The other should say "System variables". 

In both sections of the window, look for and edit (if they exist) the PATH, PYTHONPATH, and PY_HOME environment variables. 

I removed any references to Python 3. 
I set the PY_HOME variable to C:\Python27 (or whatever the path is to the Python installation you're trying to get working in PyCharm.) 

I also deleted my installation of Python27 and reinstalled it, but I'm not sure that that was necessary. 
Restart PyCharm.