Attach assembly here.
Can you add some screen shots?
When you say 'fixed' do you mean the boundary condition of the one part?
Are the parts touching & bonded or are there any gaps or sliver edges?
In a Linear Static Analysis, all parts in the assembly need to be adequately restrained in all 3 directions so that forces can generate stresses. In your model, something may not be properly restrained. Follow these steps
1. Right Click the name of the study --> Properties --> Check the 'Soft Springs to stabilize model'. Also check the 'Automatic Solver Selection' box
2. Run the study again
3. You will get a warning about large displacement --> Hit No.
4. Check Displacement plot and see which part is flying off in space
It is a possibility that there was a gap between that component and another adjacent one that is restrained. In this case, create a Contact Set to bond the two and run the study again.
Let me know if this helps