1.5.0.1 has a whole range of bugs and irritations for early adopters. From changes to the templates, changes to pear. To add to the mix there is the check out error bug that throws the error “street address must be equal to or greater than x characters”. This happens if a returning customer is attempting to ship to an existing address. They are forced to enter a new address even if it is identical to the existing address.

The work around is in the backend

System>Configuration>Customers>Customer Configuration>Name and Address Options

look for Number of Lines in a Street Address

clear this (will probably show a 2) and save

This should now have fixed the problem