The primary exchange rate server (oanda) failed
 

Quite frequently oanda fails and the xe update resets that specific currency to 0.00000:
This has been an issue for a number of months, forcing me to manually reset each failed currency. Again, this occurs quite often, and on numerous carts.

Any suggestions on how to correct this?

Thanks :)

I get the same issue, really annoying. I have 6 currencies. When I click the update currencies button two or three currencies are updated as zero. Only one with zero if i'm lucky, that's actually what I shoot for, I keep clicking the update button a few times until it only gives me one error, then I edit that one manually.

This happens with all ZC version I have 1.3.7 - 1.3.9

I think the oanda server always has issues. I meant to look into that a while ago, but I keep forgetting because I only update currencies about once a month, but it's very annoying when I have to do it with this problem.

Which is the file that defines the primary server/

If it's any consolation, the code in v1.5 has been updated to add and use ECB as the primary. Just one more good reason to upgrade ;)

This is your lucky day ... zen-cart.com/downloads.php?do=file&id=1341

ECB Currency Update Replacement for v1.3.9

This module backports the ECB/BOC currency-update facility from v1.5.0 to v1.3.9.
It is also compatible with v1.3.6, 1.3.7, 1.3.8.

Simply unzip, and take the two files in the archive and upload them to the corresponding folders under your renamed-admin directory.

NEW FILE:
/admin/includes/extra_configures/v13X_ecb_currency_enabler.php

REPLACES FILE:
/admin/includes/functions/localization.php