Moving data to the NX4 from Windows servers

Please forgive me as I am very new to this. We have purchased an NX4 and planned on migrating our data from Dell servers to a share on the NX4 box. We currently have 3 shares set up and I have been successful in moving most of it. I am using Retrospect backup and restore to move the data, but unfortunately, roughly 500gb of our 2tb to be moved gives errors and does not move to the NX4. I'm not sure if there is should be another way that I should try, yet the 20k that I would be charged for data migration by EMC seems steep. This also leads me to worry about the backup solution I have and if any data from my prodution network will have these errors. Please let me know if there are better tools to do this migration that I should know about. Thank you in advance for your help.