When you set up econnect to use with web services you need to have all the ISO codes for your individual currencies in Dynamics (GP) populated.
These are setup on the currency maintenance window in Dynamics (GP).
There are two internationally recognised codes for each currency. An alphabetic and a numeric code. Please be aware you need to use the alphabetic code as the web services will not pass/recognise the numeric ones.
The below ISO website has the list of internationally recognised codes.
If you have any questions contact firstname.lastname@example.org