In Zen Cart 1.5. I am getting the error message when posting to Authorize.Net.

(TESTMODE) The supplied currency code is either invalid, not supported, not allowed for this merchant or doesn't have an exchange rate. - Your credit card could not be authorized for this reason. Please correct the information and try again or contact us for further assistance.

However, Dr Byte has affirmed on this thread,

http://www.zen-cart.com/showthread.php?187287-Done-v1-5-0-1-5-1-Authorize-net-AIM-module-currency-code-invalid-for-GB-UK-customers

"The AIM module in v1.5.0 automatically converts prices into USD before submission, so that transaction amounts are submitted in their USD equivalent (based on your store's exchange rate data)."

I have looked at other threads, some advising editing the authorizenet_aim.php for global currencies

global $currencies;
$usd_transaction_value = $currencies->value(number_format($order->info['total'], 2), true, 'USD'
and
'x_amount' => $usd_transaction_value,

but this appeared to make no difference.

This is now an urgent issue, so any help on updates on this issue would be appreciated.
Thanks

Turn on Debug-Log-To-File (or to email) in that module, and then do a test transaction. Then post the log file's contents here.
Also, contact your Authnet account representative and confirm what currency your account is configured for. They recently added support for additional currencies (for different countries), and if your account isn't configured for the currency you're submitting, you'll get errors. If your rep says it's configured for something other than USD, then some coding changes will be required to accommodate that: https://github.com/zencart/zencart/commit/d0e3100a2ee91a0cbae90cd10d5c0319a9933be7

hi Thanks for the reply.
Here is the autorizenet log file.
I haven't had a reply from authorize.net regarding the currency set up for my account.
I have removed my phone, address and email field data as these are not an issue.

May-03-2013 12:29:41

Response Code: 3.
Response Text: (TESTMODE) The supplied currency code is either invalid, not supported, not allowed for this merchant or doesn't have an exchange rate.

Sending to Authorizenet: Array
(
[x_login] => *******
[x_tran_key] => *******
[x_relay_response] => FALSE
[x_delim_data] => TRUE
[x_delim_char] => |
[x_encap_char] => *
[x_version] => 3.1
[x_type] => AUTH_CAPTURE
[x_method] => CC
[x_amount] => 1.49
[x_currency_code] => USD
[x_card_num] => XXXXXXXXXXXXXXXXX0027
[x_exp_date] => 0613
[x_card_code] => ****

...

I should add that the site is in UK, and set up for GBP
https://www.romseybaitandtackle.co.uk/

You'll need to make the coding changes I mentioned in my prior post.

Very many thanks Dr. Byte.
Although my 2 files were not exactly as you show on Github, I was able to make the appropriate changes, and the payment passed through to Authorize.net.

Kevin