Navigator unusable because it doesn't find Ext. SD-Card any more

Hello,

I posted this in another thread already (http://forum.mapfactor.com/discussion/7065/map-update-issue#Item_9), but meanwhile I believe that this is a different problem. That's why I open a new thread now. Additionally I had to expand the description in the end because the problem continues after I thought I had fixed it.

The problem started after one of several map updates failed, but this might or might not be the cause of the problem.
I have only OSM maps installed. My phone is a Samsung XCover 2 with Android 4.1.2

1. Notification of updates -> chose to download them.
2. During
   the last of several updates something went wrong, app said connection
   was interrupted. (Okay, that may happen.) Chose to make the last update
   some other time and closed the app.
   
3. Next morning started the
   app. First error message something like "No access to external SD card.
   Maybe due to system update to Android 4.4?" and as I dismissed it
   second message: "No maps installed. Download?"
4. I choose not to
   download, because I know they are on the device. I want to go to
   settings and check if the app remembers correctly that they were stored
   on the SD card. (Which is by the way perfectly accessible and I'm still
   running 4.1.2.) App exits, no way to interact.
   
5. Restart app,
   choose download, so that I can somehow enter the app. Barely space on
   internal memory, luckily for Andorra + the mandatory earth.osm it is
   enough.
6. Now I can go to settings. Strangely the folder where my
   old installation including more than 1GB of data resides is identified
   as "Internal Memory" and the one where navigator moved itself just now
   as "External SD-Card 1". (I believe I realized this error before when I
   had chosen the so-called internal memory after my first installation of
   the app.)
   (<- This is how I found the settings. I had chosen the opposite.)
   I
   change the path back to so-called internal which is external really and
   close the app. It says it deletes some invalid data and exits.
7. After
   restart it says for quite some time it verifies the integrity of data.
   But after some minutes and a restart it seems to work.
8. Verified that the app works correctly
9. Start the app again later that day to use it for navigating -> initial problem. First it complains that the Ext. SD card is write protected, later on it doesn't find it any more.
   

Result: Can't use Navigator any more at all.

Are there different ways an SD card can be mounted? Can anything have changed that is a problem for Navigator but not for other apps? Everything else works as normal as far as I can tell.

Any help appreciated!

Joachim

(All messages' wording may have been different. My system is German and I didn't immediately take notes.)