Cortex-R5 MPU: writing to Region Base Register randomly causes Abort Exception

Hi all, I am using MPU of Cortex-R5, in doing so when writing to Base Register, via standard CP15 access. (MCR p15, 0, Rd, c6, c1, 0) it randomly causes Prefetch Abort Exception, i.e. sometimes it works fine aswell. and IFSR shows PERMISSION type fault.