Lion Install Fails on 2009 MacPro

I am running a 2009 MacPro 2.94 Ghz Quad-Core Intel Xeon. 8 GB of RAM. Plenty of hard drives and capacity. I have repeatedly tried various fixes to upgrade to Lion from 10.6.8 Snow Leopard and they all fail at the same point. I've attempted upgrades, a clean install to a new drive, created an install flash drive with Lion (which btw worked to upgrade an MacBook Pro), but just can't get Lion installed on the Mac Pro. I have re-downloaded the Lion install several times to ensure I have a fresh, working copy.

The problem manifests as follows:

1. Lion installer launches fine.

2. Takes about 3 minutes and tells me it will automatically restart my computer

3. Restart happens, then eventually the Lion grey screen opens asking me to select a language - pick English

4. Lion recovery screen opens next showing things like Disk Utility and gives you option to Re-install Lion. Have no other choice so select re-install

5. Lion installation screen opens and tells me it needs to download additional components - usually takes about 3 minutes again

6. Computer restarts

7. Computer re-opens back to step 3 again and once again, I can only really chose to re-install Lion

8. This time I get an error message that says the Install Copy of Lion is damaged and cannot be used to install Lion

9...... Rinse, repeat, fail again

Its like an endless loop where it tries to install, then downloads additonal components (no idea which), and then concludes that the install copy of Lion is damaged (suspect because of the dowloading of additional components)

Any help would be much appreciated

Ec