custom format changes to special

[Jan S]

I need to regularly reformat numbers in cells into a custom number
(000000000). I create a formatted cell and place a number 1 in it
(000000001). I thne copy it and use paste special multiply. This has work
great reformatting cells until this week. I tried it and now the cell
formats itself into Special Social Security (Portuguese) format. It changes
all of the cells even the orginal. Any ideas? I can not change it back. I
need the formatting to help with vlookups

Thanks
Jan