I think you should better explain your scenario, but looks like you have a different "Current Directory" in the server.
When you open your StreamReader you have a relative path, which is perhaps being interpeted as being relative to the Environment.CurrentDirectory.
I'd suggest 2 solutions:
Get your executable directory and combine that with the file name to get a full path (see here)
Assuming that by scheduler you mean the Windows Task Scheduler, you can set the start directory in your action definition: