Error in Developers toolkit

Hi, I’m trying to make an upgrade from a customized version 3.60 to version 4. I’m only interested in making the upgrade of the objects. I follow the following steps: 1. Create a new base Version 4.00 on Developers Toolkit. 2. Then restore a backup of 3.60 base version with the client of version 4.00 and export all objects to text file. 3. Did the same to our 3.60 customized version. 4. Remove the IDs from the two last files and then create two new versions in the Dev toolkit and import the two files. 5. I start the Merge wizard, choose the correct versions, and give a name to the new custom version. Choose for action Merge, in Focus on Objects in I choose All versions. I thin those are the correct steps to start the upgrade. But every time I choose finish I always get the following error: ‘’ is not a valid integer value. I can choose other options but I always get the same error. Anyone have some ideas about it? Thanks in advance, Mestre