To ensure service levels and quality, Salesforce imposes an API usage limit on its customers. Salesforce organizations are subject to a maximum number of API calls that can be made against Salesforce servers in any 24-hour period.
To monitor your API usage, log in to Salesforce, and choose Reports > Administrative Reports > API Calls Made Within Last 7 Days.
The Salesforce ODBC driver uses the Salesforce Web Services API to connect to Salesforce, and is therefore subject to the API usage limit.