Automation Error - Thrown Out of Excel

[Joakim N]

Hi,

I'm thrown out of Excel without warnings. It occurs when I open a form inside another form:
- If the 1st form is open in background --> I'm thrown out of Excel when I close the 2nd form. No warnings.
- If the 1st form is closed (Unload Me) before I open the 2nd form --> Everything is OK (I show the 1st form again when I close the 2nd form)

I have opened forms inside other forms in multiple applications before. No issues at all. It's only in this specific application. That's why I'm confused.

I've tested to add DoEvents, Application.Wait, ... in the code in specific locations but nothing seems to help. Sometimes I get following message before being thrown out of Excel. I've added a picture file.

Has anyone experienced this issue?