Update:
1. Log with c:geo (what a bad word ?) => no clue
2. Delete Log on gc.com via PC/Firefox und log again => no clue
3. Delete Log on gc.com via PC/Firefox und log again => no clue
4. Delete Log on gc.com via PC/Firefox, install original GC App und log again => clue
This is not what I expected. If you want to keep all us c:geo users out, just let us know. But why doesn't it work on gc.com website?