Paolo,
Your issue is caused by line 56 on 04webassist_Update.php which reads:
$WA_columnTypesStr = "undefined";
This should read something like:
$WA_columnTypesStr = "',none,''"
for a text based field.
Try running the wizard again and if you still get the same results then I would suggest that you need a WA engineer to look at the issue as it may be something in your set-up that is causing it.