can't open protected xls, Arguments window weird

With MS Office for Mac 2008 on a late 2011 MacBook Pro, I can open other .xls files, but not one that is PW protected, although I know the PW. When I try, what appears to be broken message window appears. It shows only the top half of a window, with now red/yellow/green buttons and the bottom seems truncated. On the top it says "Select Arguments" Inside, there is what appears to be an up arrow in the upper left corner. It says "[filename].xls" is protected. Arguments: "

If I type in the PW or try to move the slider on the right, the window closes and a new message says the PW was not correct and to check Caps Lock.

If I Preview the file with Quick Look, I can view it after I enter the PW, but I cannot edit it. I wonder if this is an upgrade to Yosemite issue of if this particular file has been corrupted. Do I have any option other than to recreate the file from scratch using a screenshot taken from the Preview.

If I Preview the file with Quick Look, I can view it after I enter the PW, but I cannot edit it. I wonder if this is an upgrade to Yosemite issue of if this particular file has been corrupted. Do I have any option other than to recreate the file from scratch using a screenshot taken from the Preview.

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I would guess the Excel file is corrupt. Upgrading to Yosemite would not effect the file unless the entire upgrade was bad and then it would impact much more than a single Excel file. You might want to run Disk Utility from your recovery partition and verify the hard drive before pressing on and trying to re-create the file.

I should also add that password protecting Office files sometimes is hit and miss. I've seen problems with file protection even with the Windows versions of Office.