I believe it is a generic error. It is hard to solve the issue without looking actual workbook.
What I will do
1. Can you see data in all the worksheets?
2. I will publish worksheets separately on tableau server.
3. I will bring one worksheet on the dashboard and then publish it on the server.
I think, one or more worksheets have some problem and due to this whole dashboard does not load.
hope this helps
Thanks Arvind. That's what I tried. There was some issue with a data source. I was able to see the data but on server it had some issues. Not sure what exactly. I just closed that Data source and created another one with the same custom sql. It worked like a charm! Thanks again.