Last year I was assigned with someone X (who I report to him) to a task (develop an application from scratch). This task needed lot of development and tests and many changes happens on the go. Person X changed to another department, and I continued developing this task.
Later on the executive asked my manager to take this task from me (because it is critical) and he continue developing and test it. I am not involved anymore in this task. I asked my manager why this happened, and he replied that it's because it is critical and he found some bugs in it, but the full complicated process is working. He said the executive just doesn't trust your work. I explained that since I spent a year developing and fixing things in it and the full process is working, I was waiting for a compliment even a raise from this for the hard work. He made me feel like I failed with this task.
In any case, I forgot about the task, and I focused on improving my skills. Later on, some modifications on this task were needed and my manager asked me and my coworker to work on it. My coworker started working on it, however next week he is going on a vacation and asked me to continue on it especially because I am familiar with it.
The problem is that I am not interested in working on this task anymore. If I am not taking credit for it, he didn't want me to be involved and they don't trust my work, the why do I have to continue working it?
So how can I tell my manager that I am not interested in this task so that he doesn't take it a negative way?