[ic] Download error

[DB]

Recently I'm getting complaints of customers being unable to download
purchased items (pdf files). I did a test purchase and all seems OK if
the buyer is logged into an established account. If however they check
out without first creating an account, the purchase completes - but when
they click the Download button from the receipt page, this error is
displyed:

Sorry, there was an error in processing this form action. Please report
the error or try again later. (Can't locate object method "new" via
package "Vend::UserDB" (perhaps you forgot to load "Vend::UserDB"?) at
/usr/local/interchange/lib/Vend/UserDB.pm line 2008. )

I see no errors in my IC logs or in my web server logs. I do see a 200
for the pdf in the web server log. I don't have much to go on... does
anyone have any thoughts? This is 5.6.3 using a modified foundation store.

DB