MS SQL 2012 and SSISDB

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SQL-Server-2012

I have a piece of C# code that I used to query a database. Today I used the same code (few minor changes db names, columnNames...etc) to query the SSISDB but failed as the SSISDB cannot be opened as requested by the login. so I tried the following:
1. run the query against the SSISDB from within SSM studio-worked fine
2. Then using the command osql -Usa -Ppassword
>sp_helpdb: This returns all DBs including SSISDB
but when I type
>use SSIDB
>go
an error display that SSIDB does not exist
I used both windows authentication and the "SA"
So what is going on with SSISDB???
any help is greatly appreciated