I have recently spent some time looking into an issue where my K2Workspace account was not able to connect to SQL Server.

This manifested itself as:

In the workspace the following error:

- Membership could not be verified

In SQL Management Logs as:

- Error is 18456, Severity: 14, State: 11

Resolution:

To resolve this issue we first looked to validate that connect rights were given to

1. The account itself
2. The roles the users were members Of

Finally it turned out that the public role did not have Connect rights for TCP communication as shown below

I hope this helps someone