The "Paste" toolbar tab in Excel Office 365 suddenly ceased functioning! The "Cut" an "Copy" tabs continue to function normally; however, the "Paste" tab remains "grayed out" (all the time) and does not respond! I am able to Cut or Copy and Paste by placing the cursor over the destination cell and pressing "Enter;" however, the "Paste" tab remains inactive ("grayed out")! I just noticed this problem this morning, 09/25/2019. I ran my anti-virus/malware programs--no threats detected, and have not knowingly updated my Windows/Office 365 software recently. Can anyone help?