Sharing files between PC and Mac cannot be edited.

I am required to send expense reports to my boss from my mac computer, he has a pc. I use numbers, but save a copy as excel and everything shares well. However he cannot edit the files. On my end all of my preferences are "read & write". Also we are connected to the same server. Any ideas what could be wrong?

Thanks.

When he receives the files are they read only? In other words, what's preventing him from editing them?

He can edit them, but when he attempts to save he gets an error message saying he doesn't have permission to save it as the same file, thus he would have to make a copy.