Bulk Uploading Contacts into Facebook - How Do I Get it to Work?

I am a group Admin on Facebook with 1500 contacts on a .csv spreadsheet I want to invite to our Group. Every time I try to upload these contacts into Facebook using their import feature, Facebook hangs, and then delivers an error message. It seems to only import some of the contacts not all - so I have no way of knowing if it has imported all and is sending out invites 100 at a time, or if it timed out and didn't import all the data in my spreadsheet.

I've tried importing the spreadsheet directly. I've even opened Yahoo & Gmail accounts and tried importing those contacts that way. This also happens when I try to upload them directly into my profile, so I can invite them to the group as "friends" - though I prefer to keep my biz contacts and friends separate.

Any idea how to get this to work? It's very frustrating and time-consuming.