And what does the log say?
Suppose you have a multiple condition step based on the value of container element X
and it can either be 1, 2, or 3
Now in the log you can see that value of X is empty or 4 or something else. Then the workflow will go in errror since it doesn't know which branch to take.
There is no easy answer for your issue, you have to delve in the workflow log along side the workflow definition to understand what has happened and how to fix it.
Kind regards, Rob Dielemans