Q:

I was assigned to a fake project after being hired. Is this bad news for my career?

I was hired as a senior software developer and was briefed about a project while interviewing at a client. When I officially started with this company, something went wrong. Eventually, the client declined my CV, and, from then, I started to feel that something changed.
I was doing absolutely nothing for 2 months. Suddenly, a manager assigned to me an internal project, saying it is intended to ease the work of managers. I worked on the project relentlessly, until I achieved the objectives. That's when it was decided I will be staffed at a different client that uses the same technological stack.
At the end, the manager who was in charge of project didn't want the source code or anything from my project. That's when I realized it was a fake project.
Is it bad news for a senior developer to undergo such a process? Or was it legitimate?

A:

Stop worrying
You were assigned to work on internal project XX in part because you had nothing better to do.
You are now assigned to a client using the same technology stack.
It sounds to me like project XX was a successful training project.  
That's not fake and it's not bad news for you.

A:

Is it bad news for a senior developer to undergo such a process? Or was it legitimate?

You'd know it's legit by getting paid. If you don't get paid, then worry. Companies are not going to hold a ultra secret conspiracy against you. They're either going to pay you or fire you. No secret agendas. 
As always keep your resume up to date and ready. There are no guarantees with anything and you'll always want to keep things up to date in case.  

