Vdata installation issue
To transfer data from Joomla 2.5.x to Joomla 3.x you do not need to install vData on Joomla 2.5.x version. You can do so with Joomla 3.x itself. Please follow the below steps:
1. Install vData on Joomla 3.x
2. Go to vData configuration and enter the Database details of Your Joomla 2.5.x site, Now It would consider your Joomla 2.5.x database as It's localhost database.
3. Please export all the data whichever you want after create profiles as per your requirements.
4. Once data is exported, Go to vData Configuration and Tick Local Database option, It would again work with Joomla 3.x Database.
5. Now you can import the exported Data, It would be installed in Joomla 3.x site.
Hope I could explain it precisely. Please let us know if you have any queries. Would be happy to assist.