Cant reboot into custom recovery!

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http://forum.xda-developers.com – I rooted my phone by odin method . Flashing clockwork mod recovery over stock recovery . And somehow I was able to install Superuser. But now when I try to reboot in recovery it takes me to stock recovery mode not custom recovery. I tried both recovery and they work for a while and after some time they dont. Why is this happening ? Su is working fine and I m on UVLH2 . Thanks in advance Sent from my SGH-T999 using xda premium (HowTos)