With two foreign and two domestic focus cities, you have already exceeded your allotment of available focus cities. Not sure how you did that.
With the [?] 5 setting, you are allowed the following combinations...
* Five domestic
* Three domestic & one foreign
* Two domestic & one foreign
* One domestic & two foreign
The infinite focus city setting there is somewhat of a misnomer, as you can actually only build up to the number of domestic focus cities allowed.
If the setting was something like, [5] ?, then you could build five foreign focus cities without worrying about running into the issue you are experiencing right now.
