Artboards disappearing in Illustrator CS4

i'm using illustrator cs4 on mac osx 10.6 , have created 12 page document folks @ work.

every time re-open document make amends first artboard have disappeared.

all artwork content still there, layers fine etc outline of artboard page there guides added layed named 'guides artboard'.

when create pdf of file one, first page. it's doesn't realise rest of pages exist.

but doesn't happen every document. keeps happening one, it's happened others when open them again later fine.

is bug??

this file created new in cs4 , edited myself on same machine.

any suggestions save me serious grief!!

you're sure, didn't accidentally save ai cs3?

More discussions in Illustrator

adobe

SPI