Error List does not exist

Hi all, I am working on sharepoint 2010. I have created a list work flow in Share Point Designer 2010.

in the first step I put an 'If any value' condition and put email, and to-do in it, deploy and run the work flow it works fine.

later I change the work flow and put email, and to-do to run in parallel activity, deploy and now when I tried to upload a file in the document library its giving me following error.





List does not exist.

The page you selected contains a list that does not exist.  It may have been deleted by another user.





can some body tell me why I am getting this error...