Seeing as how Excel is not an Apple product but a Microsoft product, you would probably have better luck getting an answer over on the Microsoft forum and certainly not on the Appleworks forum.
Currently Being ModeratedJul 24, 2012 10:26 AM (in response to Brad87)
This forum is dedicated to Apple’s now-abandoned productivity application, AppleWorks. It is not a "catch-all" for how Apple computers work. Your question is best asked in Microsoft's forumns.
Currently Being ModeratedJul 24, 2012 11:17 PM (in response to Brad87)
I'll join the chorus, after a note on this comment, which caught my eye:
"when I try to access it later, it makes me resave it again because it says it's read only."
Are you, perchance, using OS X v10.7.x (Lion)? If so, finding a file locked when you try to access it later could be due to a new feature in Lion, which locks files that have not been used for a while. You can set the length of "a while" in System Preferences.
If that's not the cause, click the link in Peggy's message. It'll take you to Msoft's Mac forums, where you'll find users more familiar with the vagaries of Excel.