Steps to reproduce:
1) Create a new project (important).
2) When the project is open in Unity, press ⌘+B on Mac or CTRL+B on Windows.

An error appears in the Console:
UnityEditor.BuildPlayerWindow+BuildMethodException: Build location for buildTarget StandaloneOSXIntel64is not valid.
at UnityEditor.BuildPlayerWindow+DefaultBuildMethods.GetBuildPlayerOptions (BuildPlayerOptions defaultBuildPlayerOptions) [0x001cd] in /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPlayerWindowBuildMethods.cs:224
at UnityEditor.BuildPlayerWindow.CallBuildMethods (BuildOptions defaultBuildOptions) [0x0002e] in /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPlayerWindowBuildMethods.cs:78
UnityEditor.BuildPlayerWindow:BuildPlayerAndRun()

The Build Settings window can still be opened using ⌘+Shift+B or CTRL+Shift+B or via menu bar.
After this is done, ⌘+B and CTRL+B starts working as well.
If the project is closed and reopening, the bug disappears.

Expected result: Build Settings window pops up.
Actual result: Error appears; the build window doesn't appear.

This happens on both macOS and Windows with all platforms selected (iOS, Android, Standalone).

Reproduced on:
2017.1.0b4, 2017.1.0b1, 2017.1.0a6

Did not reproduce:
2017.1.0a5