Pagefile on C:\ drive disappears

This is a weird problem to which I have yet to find a definitive solution ....

Running XP Pro SP2 patched up to the eyeballs

My main pagefile is on a dedicated partition on my third hard drive - SATA

I notionally have a fixed 500Mb pagefile on the root drive C:\ for memory dumps, but this keeps on disappearing. In Device Manager the pagefile is shown against C:\ drive, but NOT in the Total Paging File Size for all drives. If I hit the set button with C:\ selected and reboot the pagefile will show up on a FileLocator Pro search or on Doug Knox's Page File Monitor for a while and then it is gone again.

I triple boot to XP Pro SP2 (daily) and occasionally to XP Pro x64 or Windows Vista. I suspect one of the other OS's is mucking around with the C:\ pagefile. The Filelocator Pro search shows the dedicated pagefile on the SATA drive for XP Pro SP2 and the pagefile for Vista (Set for the OS drive only) - the x64 pagefile is not shown in the search, but this is understandable if it is essentially 64 bit which FileLocator Pro probably does not read.

Any thoughts on this?

 

XP Pro SP2 I guess - that's the first on the list and the default OS to load.