Error message when trying to clip layers

[RichardOvery]

I am using Arc 9.3.1 and have been trying to clip one polygon layer from another (using Arc Toolbox, extract, clip). The following error keeps displaying. Warning 000632: Datum conflict between map and output.

I have carried out this type of clipping using one layer to cookie cut through another before without problems. Can anyone help?

Thanks

[TomLewis1]

I seem to be having the same issue in Arc 10....