Bit of MSSQL Code need help with

All

I have a sql server, with two databases on. I want to copy two columns with data from database B to database A as below:

USE Database A;
Insert into cases(CaseCode, CaseName)
Select casecode, name FROM DatabaseB.TableA_case;

It errors on:
[Err] 42S02 - [SQL Server]Invalid object name 'DatabaseB.TableA_case'.


I know I need to use the table somehow, but am unsure what to do, can anyone help?