Internal Server Error occurs when access to Classic UI

You may see Internal Server Error when accessing to Classic UI.

This issue occurs when [Your Invoice] tab exists in your application, and [All Tabs] application is used for the user.

Workaround

1. Use Lightning Experience UI.

2. Hide [Your Invoices] tab from the user by profile or permission set.

3. You can access to Classic UI temporally by accessing to the following  type of URL:

4. https://[mydomain].my.salesforce.com/001/o

   https://[mydomain].my.salesforce.com/lightning/page/home

   https://[mydomain].my.salesforce.com/?isdtp=vw