Couldn't open device I can not partition nor use a removable USB disk without file system.
I obtained the following informations:
sh-3.2# diskutil info disk2
   Device Identifier:        disk2
   Device Node:              /dev/disk2
   Whole:                    Yes
   Part of Whole:            disk2
   Device / Media Name:      IC1100        CF

   Volume Name:              Not applicable (no file system)

   Mounted:                  Not applicable (no file system)

   File System:              None

   Content (IOContent):      None
   OS Can Be Installed:      No
   Media Type:               Generic
   Protocol:                 USB
   SMART Status:             Not Supported

   Total Size:               8.0 GB (7994327040 Bytes) (exactly 15613920 512-Byte-Units)
   Volume Free Space:        Not applicable (no file system)
   Device Block Size:        512 Bytes

   Read-Only Media:          No
   Read-Only Volume:         Not applicable (no file system)

   Device Location:          External
   Removable Media:          Yes
   Media Removal:            Software-Activated

   Virtual:                  No
   OS 9 Drivers:             No
   Low Level Format:         Not supported

After following this guide, I am now able to see the disk in Disk Utility, but it is uninitialized, and when I try to format it, I get the error
Couldn't open device
EDIT: I tried the following:

Disk Utility &gt; Erase
Terminal &gt; diskutil eraseDisk MS-DOS NAME disk2
Terminal &gt; diskutil eraseVolume MS-DOS NAME disk2
Terminal &gt; diskutil partitionDisk disk2 1 MBR MS-DOS NAME 7.8GB

They ALL lead to the same error: Error: -69877: Couldn't open device
EDIT 2: This is the partition table:
    sh-3.2# fdisk -e /dev/disk2
    fdisk: could not open MBR file /usr/standalone/i386/boot0: No such file or directory
    The signature for this MBR is invalid.
    Would you like to initialize the partition table? [y] y
    Enter 'help' for information
    fdisk:*1&gt; p
    Disk: /dev/disk2    geometry: 971/255/63 [15613920 sectors]
    Offset: 0   Signature: 0xAA55
             Starting       Ending
     #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
    ------------------------------------------------------------------------
     1: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
     2: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
     3: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
     4: 00    0   0   0 -    0   0   0 [         0 -          0] unused
 

EDIT 3: If I type fdisk /dev/disk2 , this is shown:
sh-3.2# fdisk /dev/disk2    
Disk: /dev/disk2    geometry: 971/255/63 [15613920 sectors]
Signature: 0xD913
         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
 1: D5  843 125  41 -  856  48  15 [3289417632 - 1579849264] &lt;Unknown ID&gt;
 2: B0  380 233  63 -  580 252  34 [1433382022 - 2359874114] &lt;Unknown ID&gt;
 3: 21  542 173  50 -  368 171  22 [ 805962412 - 2236752874] &lt;Unknown ID&gt;
 4: C1  311 233  33 -  417  95   7 [3864719105 - 4292535645] DRDOSs FAT12

How can I solve? Thanks
(I'm using Mac OS X 10.11.3)
Restore a DMG (maybe an OSX InstallESD.dmg or any other application) to the disk/drive via Disk Util. This will overwrite it (deleting all data). Then you can partition again how you like.

I have encountered this several times myself with USB pen drives as well as SSDs inside a MacBook Air. Formatting and Erasing brought up the exact same errors you describe. DD didn't work out, Resizing the partition gave me an error about corruption on the disk. First Aid/Scanning &amp; Repairing the volume didn't yield any results, the tool completed with the message that there wasn't anything to repair.

Only the Restoring of a random DMG to the drives made it manageable again.

Hope this helps!