I have a user account on a clients Salesforce. These credentials are used on our Web service to connect and upload data to that clients Salesforce account.
However I have found that only my PC will allow the logging in to the API, this is not ideal as I need to have multiple users logged in using the same account and on different PC's in our organisation.
How can I fix this issue?
a review of their policy suggests that what you want to do is prohibited, however it seems that it should be possible. There is a way to lock the account to the ip that created and perhaps that is being used as a default. please have a look here and see if it applies to your situation. https://help.salesforce.com/apex/htviewhelpdoc?id=admin_sessions.htm&language=en_US
As you have found, you need to append the Security Token to the password to allow API logins from IP addresses that aren't trusted. This is a fairly standard way of calling the API. Note that changing the password will also change the Security Token.
The alternative to using the security token is to add the IP addresses of the Server making the API calls to the Trusted IP ranges.
Setup > Administration Setup > Security Controls > Network Access
