There might be several reasons for this.

First check out whether the Informatica service is running or not. Sometimes the server address will change everytime.so it is suggestable to resolve the server (server-server configuration) and then start the service.

Also check out the repository server configuration...

hope this will be useful..

Try to folow the below mentioned steps ...

>Configure the Informatica Server Set-Up in Start-->Programs-->Informatica7.1-->Informatica server set-up.

>Open the the workflow manager go to workflow tab and then assign server option.

Put the server name that you have given in server set-up.

>Then go to control panel-->services and start the informatica server service.

Then do the things.. Most probably will work great.

First check the Informatica service is running or not.

2nd the server address will change everytime.start the service.

Go to workflow Manager- Server-Configuration

and Last see repository server configuration...