The old IBM System X servers that still use the IMM v1 with the latest firmware has an unpatched bug, making the Web GUI inaccessible with any recent browser.
The bug is known, but the affected hardware are quiet old, so it is not going to be fixed. Instead there is a workaround by enabling HTTPS.
To do this without the Web GUI is not trivial, you have to download and use the IBM Advanced Settings Utility.
I had to apply this workaround to multiple servers, so I just created a small script to make my life easier.
Use it your own risk!
As I'm currently working for IBM, please read my disclaimer.