Vmarna, Just out of curiosity do you have those Virtual Disks being accessed by multiple systems? If so are they set up into a cluster environment? Also here is a link that  breaks down the steps for setting up the MPIO for iSCSI initiator. Just to make sure none of the steps may have been skipped. paulgrevink.wordpress.com/.../configure-dell-md3000i-mpio-with-windows-2008-r2 I hope this helps. Feel free to let me know if you have any questions or concerns.
Hello, I´ve configured MS ISCSI Initiator in Windows 2008 R2 Enterprise with SP1. There are 2 NICS for comunication with DELL MD3000i and from Modular Disk Storage Manager I've added the host and assigned 2 virtual disks to the host. (LUN 1 and LUN 2). One of the virtual disks works fine from the Disks Administrator of W2008. The other virtual disk appears but I don´t work with him. I can´t assign letter. I can´t switch it ONLINE or INITIALIZE because appears ERROR. This same virtual disk can be assigned to another host without problem. The problem can be ISCSI Initiator?  After doing changes in ISCSI Initiator I can work fine with this virtual disk and the problem appears in the other virtual disk.   Any idea?  
MS ISCSI Initiator MD3000i VIRTUAL DISK NOT RECOGNIZED