One user of many cannot paste anything after cutting or copying (regardless
of shortcut key, ribbon, right mouse menu). Problem just started this week.
Paste option is greyed out.

He can copy between worksheets but not workbooks.

Tried running Excel in safe mode in case macros caused the issue. No luck.

Apparently the workbooks are being opened in different instances of Excel.

To test open the first file and then use Office Button-Open option to open
the second file...

If it works then do the following to fix;

Close Excel first and On the Windows Taskbar

1) Start-Run- excel.exe /unregserver -OK.
2) Start-Run- excel.exe /regserver -OK.

See the space between exe and /regserver

You might have to designate a full path to excel.exe (most likely C:\Program
Files\Microsoft Office\Office12)

In that case Start-Run- "C:\Program Files\Microsoft
Office\Office12\excel.exe" /regserver - OK

Note that quotes are required because of spaces in the path
"Richard" wrote:

One user of many cannot paste anything after cutting or copying (regardless
of shortcut key, ribbon, right mouse menu). Problem just started this week.
Paste option is greyed out.

He can copy between worksheets but not workbooks.

Tried running Excel in safe mode in case macros caused the issue. No luck.