We are in the process of upgrading on of our clients from 2.6 - 3.7. We are using Developers Toolkit 1.04. We’ve merged the databases and manually corrected conflicts. Then we’ve created a textfile to import into the new version and here is the problem. The texfile created seems to contain errors since the import always stops at some point with errors. The import seems to stop on customizations, i.e. new keys or new code. Has anyone had a similar problem? Is there any solution to this problem?
Make sure that you use the most actual 3.70-Client for access to your database and import of .txt-files. I once experienced similar problems after upgrading some objects with DevTools 1.04. Since the import tells you the # of the faulty line in txt-file, open it with a text editor that is capable of showing line nos. and correct the line manually. Look in the txt-version of other objects for the correct syntax. …and of course, after importing the corrected file into Navision, compile and check the objects for correctness of your changes.
In fact the process of just getting one object from the database into the developer toolkit and then exporting it from the developer toolkit can create a file with errors. When importing the objects something really useful is a good text editor (like Ultraeit32) for correcting the different errors on the object. Example: when the line created is longer than 250 characters the way the developer toolkit handles it may give some errors on the keys and other places. 
Just patience and a bit of extra work