System Error in Design Tab

Are there any code blocks in your template?

Where there any Web Parts in the Zone1 you now removed?

Did the error only show on the Design tab or also on the Page tab and/or live site?

If you only added and removed the zone, try clearing the Cache in the System application.

Hi,
There is an article available on this error - The Controls collection cannot be modified... error.

It could be either layout or web part issue. Could you please uncheck following property to let the Design tab to load just the layout?

Hi David there are no code block in the template. I only add editable text in that webpartzone. The error show only on design tab.

What is inside the other zone? Adding a zone you changed the life cycle of the web parts on the page - so maybe there is a web part with code blocks in the other zone.

@David cleaning the cache in system application doesn't resolve the issue.

@Jan I tried unchecking web part content the same error load

@Juraj the other zone contain a repeater.

and what are the repeater's transformations like? What about any custom layout of the page template? Are just the two zones (now I guess only one zone) in the layout? Nothing else?

@Juraj no there are other webpartzone in the page. It is basically a whole page then I put the webpartzone in editable text in the page. My repeater is loading data using this syntax <%# Eval("Text") %>. Does it have to do with other webpartzone? I also ensure they have unique ZoneID within the page

Well, the code blocks can break the page - it may work in some cases, but adding new web parts or zones changes the life cycle so the code blocks ca break it. What I am not clear is " I put the webpartzone in editable text in the page" - is it a typing mistake or how did you put web part zone in editable text? If you are using object versioning, I would recommend restoring some previous version of the page template. After removing the zone - is the layout markup valid?

@Juraj sorry what I mean is most of the webpartzone has editable text webpart only. Yes after removing the zone layout markup still valid. Page tab is working so I can see that there are no broken markup.

Not sure if it has something to do with kentico setting. I tried deleting same webpartzone in my local instance, design tab still working and the removed web part zone was shown at the bottom of the page

The problem is in staging instance btw.

If you place the webpartzone back does it work again? Make sure all Web Parts are removed from it before you delete the zone.

Remove that one with the message 'not in layout'

@David I cannot place it back in staging because it giving me the system error in design tab already

The zone definition is in your template: Go to the "Page Templates" module and edit the layout of your template.

@David it works when I placed back the removed web part zone. Okay now that I want to remove it properly what should I do?

@David sorry you already mention it how to remove it properly. It works now. I remove all web parts first the remove the web part zone. Thank you so much! It saves my day