ARRA User Migrate have few limitations in users migration from a Joomla! version to another. Is about “custom user profile fields” and languages that use diacritic letters.
1. If you have a language that use diacritics you can’t migrate users via .csv or .txt but ONLY using UTF8 tab – this include Russian Language, Chinese, Romanian, Greek….
2. If you have custom user profiles that must be migrated from Joomla! 2.5.x to Joomla 3.X you can’t use UTF8 tab but only .csv or .txt files. So, your data that contain both custom user fields and diacritic letters can’t be migrated with our component.
3. You can’t use SQL migrate between two different Joomla! versions, Joomla! 2.5 have different tables than Joomla! 3.X.