What does this error message mean - The total amount of all payments exceeds the maximum total amount for all payments?

The error message means you have used up the PayPal Pre-approved amount of $2000 (which you had approved when you subscribed to Vtiger), and Vtiger is not able to process further payments.

To add an amount of $2000 to your PayPal account:

1. Go to the Billing section. 
2. Click Replace payment method.
3. Enter PayPal details.
4. Add an amount of $2000.

To know more about PayPal, click here.