Opening Excel Worksheets

I just created an excel template for our school report cards. I have run into two problems. As I entered each student's name, I did a Save As and saved as that student. I end up with about 12 students per floppy disk. Most seem to work fine, but 1 out of 10 times, we get a messages when we try to open a student's card that says, "This file is not accessible. It may be read-only or from a read only location. It may be on a server that cannot be accessed." That is not the case. All were created and saved in identical manner so why one works and another will not is a mystery to me. I have tried opening on a number of different computers, including the original, but that does not make a difference. One teacher had entered grades and could not open it a second time to add further info. She had not changed computers. If I delete the file and create a new one, that works fine. But we need to get back into individual report cards several times and this is a major problem. No, the disks are not write protected. These are disk where all but one or two files will not open. I have tried all the usual trouble shooting. I have used excel spreadsheets for several years and have never had this problem before. As I said, all were created and saved in the same manner. I cannot find any commonality among the ones that will not open. I have 25 teachers with about 24 students each and as you can imagine, this can be quite a problem. Thank you for any help.