This may be because you have exceeded your daily Salesforce API request limit. This usually represents itself with the following error code: -5541114
To check your current API usage do the following:
- Login to Salesforce
- Go to Setup and click Company Profile, and then Company Information.
- On the Company Information screen, look for the field API Requests, Last 24 Hours
For further information on API Limits, click on the link below to go to Salesforce's Knowledge Base: