Hi,
Finally I was able to make two complete flights !! I made ENGM/ESSA (round trip). To solve this problem, I followed these steps:
1) I uninstalled IXEG 737-300 using the application Uninstall IXEG 737 Classic.exe (located in the in X-Plane´s 11 root folder).
2) Deleted the folder X-Aviation (in X-Plane 11 root folder).
3) Make a backup of your Liveries, coroutes and B733_prefs.txt (and others files you consider importants) in X-Aviation folder (located in Airplanes folder) and, then, delete this folder.
4) Make a fresh install of IXEG 737-300 1.31.
For while, I consider this issue resolved.
Thank´s for your attetion.
Best regards,
Majela
PS: Sorry if my english sounds strange and/or incorrect. I´m not native in this language...