We are using cURL (per quickstart instructions) to initiate REST API connectivity. 

When issuing the command to get a security token - https://na11.salesforce.com/services/oauth2/token - we get back the error:

Failed: API security token required","error":"invalid_grant"

Which seems odd, since we're asking for the token. The client_id, client_secret, grant_type, username, and password all look fine. 

Assuming all that information is correct, what other reasons would the app not grant a security token?

We are using cURL (per quickstart instructions) to initiate REST API connectivity. 

When issuing the command to get a security token - https://na11.salesforce.com/services/oauth2/token - we get back the error:

Failed: API security token required","error":"invalid_grant"

Which seems odd, since we're asking for the token. The client_id, client_secret, grant_type, username, and password all look fine. 

Assuming all that information is correct, what other reasons would the app not grant a security token?