Suddenly, I cannot modify and add new pipe in the model space, what is happ

[Anonymous]

Suddenly, I cannot modify and add new pipe in the model space, what is happhen?
I accidentally disable something?

[LoriWu]

Would you please provide more information about it? Did you do any special step before it?

[Anonymous]

I am not sure what step I take, but I cannot change/add any pipe, the structure is ok to change and to delete, but I cannot do anything about the pipe

[Anonymous]

This will happen when I sae the file to a new name (save as).