external loading = loading by boundary conditions.

force, snowload, prescribed deformation, ...

Please check if your boundary conditions applied as intended.

If you think that all is right and the error is still occurred, please send me your model to email.

I got in ATENA 3D the warning Zero RHS vektor.

In the Document  Troubleshooting Manual is written:
This  message  means  the  right  hand  side  of  the  equation  system  is  null,  which  is  a  consequence of having no external loading – please check if your boundary conditions applied as intended. 

What means external loading? For example snowload?
Which boundary conditions are mabye a Problem?
Whats the Problem?

Can you help me please.