RENDERD FAILED error for lookup group by column!

Hello everyone,

So here is my problem,

I created a list of client which contains a calculated (concatenate(field1;" ";field2)) field based on two other columns of the same list. Then I created another list which contains a lookup on the calculated column of the first list, then I created a view that should groups on the lookup column.... and in result I got the "<!-- #RENDER FAILED -->" for all data in view in just a single row.

Then I tried something and here is the result:
if you set the group by option to 'expanded' by default in the view settings, it renders OK. However, this is not ideal when you have a large number of groups, but better then before!

If someone can help me with explaining me what is going on I would really appreciate it.

Thanks! Shalin