Question: When I try to open a form (or project), Delphi reports a "corrupt portfolio stream" error and refuses to open the form. What's causing this and how do I fix it?
Your form's diagram file (*.ddp) is corrupted; either replace it with a backup (e.g. the *.~ddp file) or delete it entirely.

Tip: You can delete the troublesome DDP file from Delphi's File | Open dialog. To do this:

Choose File | Open from the main Delphi menu.

Type *.ddp into the File name edit box and then hit Enter.

Select the DDP file for the form you can't open.

Press Delete and then choose Yes when asked to confirm the deletion.

You should now be able to open the form.

What are DDP files?
Delphi Diagram Portfolio (*.ddp) files contain documentation diagrams created with Diagram tab near the bottom right corner of the Editor window. For more information, please see the "About the Diagram page" Delphi Help topic.