apple id not working
I have a 13 inch Macbook Pro early 2010. My final cut pro wouldn't update because of lack of memory so I updated the RAM to 8gb. After I upgraded the RAM final cut pro still wouldn't update as it said my software was too old so I updated to Yosemite. Now in the app store it looks like I should be able to update it but when it requests my apple id and password it won't allow me to enter my ID, only the password box is available to click on. (See photo for message). I have tried changing my apple ID password but it made no difference. My apple ID and password are working fine elsewhere, iCloud etc. And my other updates for other programs didn't require me to log in.
I'm not able to delete and re-download fcp as I got it for free from an old workplace and I'm can't afford to buy it. Please help!
MacBook Pro, OS X Yosemite (10.10.3)