Hi, 
I seem to have the same problem. 
I just built a 18f452 pic core and I am trying to upload MIOS. 
In MIOS Studio 2.3.1 I see the following message: 
Operating System: MIOS8 
Board: MBHP_CORE or similar 
Core family: PIC18f 
Bootloader is up & running! 
 
Then I try to upload mios_v1_9g_pic18f452.hex  
Before, during and after the upload, the MIDI IN box shows uploads requests. 
After the upload, without any errors, I still see Bootloader is up and running! 
 
How can I get MIOS into the PIC?