Excel Error: " Microsoft Excel cannot open or save any more documents....not enough available memory or space"

Open your registry:

Go to:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders

Double click to open the key "Cache"

Change from:

%USERPROFILE%\AppData\Local\Microsoft\Windows\Temporary Internet Files
to
C:\Windows\Temp

Save. Close Registry.

Log off from your windows session or restart and all should be ok now!