I uploaded the source files for 1.3.8 to an EMPTY folder.
I exported the data from an existing 1.2.6 zencart (since the templates arent compatible) and created a new copy of the database for this 1.3.8 installation.
I copied the config files from that same existing 1.2.6 zencart and altered the dbname to point at the new db. The userid accessing both DBs is the same, so I know it works (ie: the live cart still works).
All the permissions are set right.
Been using ZC for years, OsC before that.
I ended up having to upgrade manually using the sql scripts (I dont use prefixes), and then completed the install normally.
Too many people are reporting this in too many situations for it to be "just dumb user mistakes", IMO. Especially with no error messages and a blank browser page.
If you'd like the sql script of the backup so you can test privately, PM me.
Mark




