To be able to close the journals while multi-currency is enabled you will need to check a few items:

• Check that no account has a currency selected like the blog post you linked says

• Make sure you have your currency rate set correctly

• In the accounting application, go to Adviser ‣ Charts of Accounts. On each account, you can set a currency. You will have to make the currency empty so the system can handle it.

• In order to register payments in other currencies, you have to remove the currency constraint on the journal. Go to the accounting application, Click on More on the journal and Settings.

I hope these steps will help you to find where the problem is.