SQ02 query inforset the first table may not be altered

[sim_chen]

Using sq02 tcode,editing inforset.

When i change the left join into inner join,system display msg 'the first table may not be altered'.

Only cancel button,others can not do anything,no matter what button i click,always show me 'the first table may not be altered'.

How can i do to return to normal?

[sim_chen]

I change the position of the first table to the beginning of the left.Then everything OK....