Can't see altera_avalon_pio_regs.h

Need help! I have a MicroC/OS-II NIOS project that was working fine and loading to my Stratix II from the NIOS 1.1 IDE. At one point, while fixing some simple warnings it suddenly decides that it can't see altera_avalon_pio_regs.h. The project should include the HAL by default and as I said, this was all compiling and running fine.

A new install of NIOS IDE 1.1 on a different machine still produces the error even (and this is the strange bit) with the original code. The only thing I can think of is that the project had some particular setting to allow altera_avalon_pio_regs.h to be seen (btw it's in c:/altera/kits/nios2/components/altera_avalon_pio) and this was lost in the original project, but I'm clutching at straws here as this is very bizarre.

Any ideas anyone?