>>I just had this same error and it was caused by my changing the ColumnCount in the Visual Class for my grid to 2 instead of its default of -1. Once I put back the -1, the form worked right. I wasn't able to make and save any changes to the form until the -1 was put back in for ColumnCount.
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>Thanks, this means my memory is not totally out of whack :). The rule seems to be that a composite object instantiated in any container object cannot have any of its members missing, i.e. cannot have fewer members than defined in its class.

Dragan,
Just yesterday had it again. But in my case it's actually 'added' not removed. There was a pageframe where I added a new page (increased pagecount by 1 IOW) and controls in that page. No object was removed. I have a workaround that's not so smart at all:)
-Be calm. Don't panic.
-Create a temp form to copy paste 'new'
-Open code windows to copy/paste 'new' codes if any
-Close original w/o saving
-Clear all
-Open form and collect from 'pasted'
Tedious but better than losing all. And of course second time I use Ctrl+S in between:)
Cetin