Quickbooks error 6000 is caused due to multiple reason, like it can be If a customer is using an outdated software and unable to connect with the Quickbooks Account either it is due to any change in the bank password and that change is not applied in Quickbooks. In case you need more help or guidance you can simply contact Quickbooks Support Phone Number [+1(888)403-0506] for this. Sometime if a user changes the email password for email and the new password is not updated in Quickbooks it also creates this trouble which is very frustrating. If there is still an issue, please all our toll free number for Quickbooks Helpline and our technicians will help you to solve this issue.