# \[Solved\] iScreensaver Designer 4 - NSInternalInconsistencyException when open Preview window **URL:** \ **Category:** General Discussions\ **Created:** [October 7, 2015, 11:29pm UTC](https://forum.iscreensaver.com/t/solved-iscreensaver-designer-4-nsinternalinconsistencyexception-when-open-preview-window/540 "2015-10-07T23:29:56Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![fungbat](https://forum.iscreensaver.com/letter_avatar_proxy/v4/letter/f/b9e5f3/32.png) [@fungbat](https://forum.iscreensaver.com/u/fungbat)\ **Post date:** [October 7, 2015, 11:29pm UTC](https://forum.iscreensaver.com/t/solved-iscreensaver-designer-4-nsinternalinconsistencyexception-when-open-preview-window/540/1 "2015-10-07T23:29:56Z")
Hi there, I am testing out the iScreensaver Designer 4 before committing to buy a license. I have created a screen saver with only images, built an installer fine, and saved the project. However, when I re-opened the project and tried to turn on Preview window, I got the following error: A Cocoa NSInternalInconsistencyException was not handled: NSScreen reconfig must only happen on the main thread… Please report to the application developer. The application will quit now. (use NSExceptionMBS class to catch this exception) Any clue what I might have done wrong? I am running iScreensaver on Mac OS 10.10.5 Thanks, Bat ---
**Author:** ![iScreensaver](https://forum.iscreensaver.com/user_avatar/forum.iscreensaver.com/iscreensaver/32/24_2.png) [@iScreensaver](https://forum.iscreensaver.com/u/iScreensaver)\ **Post date:** [October 7, 2015, 11:34pm UTC](https://forum.iscreensaver.com/t/solved-iscreensaver-designer-4-nsinternalinconsistencyexception-when-open-preview-window/540/2 "2015-10-07T23:34:30Z")
Hi Bat, Interesting question. Can you open up the Console application (/Applications/Utilities/Console.app ) and repeat the step(s) that caused the problem? If it happens again, please note the full warning or error messages that show up in the log file. (You can also email us : support at [iscreensaver.com](http://iscreensaver.com) if the amount of info is too big to post here). ---
**Author:** ![fungbat](https://forum.iscreensaver.com/letter_avatar_proxy/v4/letter/f/b9e5f3/32.png) [@fungbat](https://forum.iscreensaver.com/u/fungbat)\ **Post date:** [October 8, 2015, 1:01am UTC](https://forum.iscreensaver.com/t/solved-iscreensaver-designer-4-nsinternalinconsistencyexception-when-open-preview-window/540/3 "2015-10-08T01:01:45Z")
Hi there, Thanks, I have just emailed what I got from the console log. Cheers, Bat ---
**Author:** ![iScreensaver](https://forum.iscreensaver.com/user_avatar/forum.iscreensaver.com/iscreensaver/32/24_2.png) [@iScreensaver](https://forum.iscreensaver.com/u/iScreensaver)\ **Post date:** [October 8, 2015, 1:50pm UTC](https://forum.iscreensaver.com/t/solved-iscreensaver-designer-4-nsinternalinconsistencyexception-when-open-preview-window/540/4 "2015-10-08T13:50:06Z")
Thanks, Bat. We’ve never seen this before, and based on the console.log info you emailed, there is something very odd going on with your system and the assertion error is in fact happening within Mac OS X itself. What we are seeing is that your system is reporting multiple Screens (displays) being connected and disconnected rapidly. Do you have an unusual setup in terms of what monitors you have connected? Are you running any third-party software that does something with displays? (e.g. remote access, display adapters that run over USB, software that uses an iPad as an external display, etc?) Our guess is that one of these things is causing the problem. Would you please also do this: 1. Open Console.app 2. If the “Show Log List” button is available, click it. 3. On the left side, under DIAGNOSTIC AND USAGE INFORMATION, look for “User Diagnostic Reports” - if you see anything with the name “iScreensaver” in it, please email us a copy of the log file. Repeat this for “System Diagnostic Reports”. ---
**Author:** ![fungbat](https://forum.iscreensaver.com/letter_avatar_proxy/v4/letter/f/b9e5f3/32.png) [@fungbat](https://forum.iscreensaver.com/u/fungbat)\ **Post date:** [October 9, 2015, 5:22am UTC](https://forum.iscreensaver.com/t/solved-iscreensaver-designer-4-nsinternalinconsistencyexception-when-open-preview-window/540/5 "2015-10-09T05:22:11Z")
Hi, Thanks for investigating. I am using a MBP and it does hook up to an external monitor once in a while via the Displayport / Thunderbolt. But at the time when I was testing the iScreensaver, it wasn’t connected to the external monitor. I am not aware of any display related 3rd party softwares that I am running. But the log file might tell a better story. I saw an iScreensaver log file under ‘User Diagnostic Reports’. I will send that across via email. Thanks, Bat ---
**Author:** ![fungbat](https://forum.iscreensaver.com/letter_avatar_proxy/v4/letter/f/b9e5f3/32.png) [@fungbat](https://forum.iscreensaver.com/u/fungbat)\ **Post date:** [October 20, 2015, 1:01am UTC](https://forum.iscreensaver.com/t/solved-iscreensaver-designer-4-nsinternalinconsistencyexception-when-open-preview-window/540/6 "2015-10-20T01:01:03Z")
A quick update from my side - after I uninstalled the iScreensaver Designer and installed it again, the problem resolves itself. ---
**Author:** ![iScreensaver](https://forum.iscreensaver.com/user_avatar/forum.iscreensaver.com/iscreensaver/32/24_2.png) [@iScreensaver](https://forum.iscreensaver.com/u/iScreensaver)\ **Post date:** [October 20, 2015, 2:37am UTC](https://forum.iscreensaver.com/t/solved-iscreensaver-designer-4-nsinternalinconsistencyexception-when-open-preview-window/540/7 "2015-10-20T02:37:11Z")
Thats… very odd! We can’t think of any reason that would fix it, but it’s good to hear that you are back in operation.