Run button is disabled in Qt Creator

I installed QtCreator 2.8.1 for test purposes and compile some project with Qt4.8.6 and Qt5.3

Result is the same as your, there is a disabled run button for Qt5 configuration and a parse problem with .pro file. Probably it's a bug.

My suggestion is to change QtCreator to latest version (everything works fine for me).

You don't have to reinstall whole qt environment, just install last QtCreator (link). It will be a separate application so you can also use the old one if needed.

Only problem is that the new installation (by default) use the same localization of settings as the old one. This may cause a problem.

I solved this by changing the default path of settings for new installation. After installation (don't run !) create on desktop (or somewhere else) a shortcut for application, right click -> properties. Under the shortcut tab, you will see an area that says Target, add at end:

-settingspath path

where path is place where setting will be placed.

for me it look:

C:\Qt\Tools\qtcreator-2.8.1\bin\qtcreator.exe -settingspath C:\Qt\Tools\qtcreator-2.8.1\settings

If new installation don't recognize both qt version and you don't know how to add it - just ask, I will add additional description.

[EDIT]

I found related question, the same problem, update of QtCreator was a solution.

I am on Qt Creator 3.6 and it still happens. The run button is disabled after project is build. The only solution is to restart Qt Creator.