Layout: Cannot change terminal from scalar to bus

Hello everyone,

I have a layout in which a scalar pin exists. Now I want to change this pin to a bus pin. But if I try this, I get the error 

Edit Properties
Cannot change terminal Name 'Vbb_lp6_PA' to 'Vbb_lp6_PA<0>'.
Error creating Terminal.

This problem I have very often. And my colleagues too.

Can anyone tell me, how to solve this problem?

Thank you very much!
Sascha