Recently I've upgraded ArcGIS Desktop on my machine - removing the 10.4.1 version, restarting the machine and installing the 10.5.1 version.
I then opened my of mxd saved under 10.4 - all went well. When tried adding a toolbox created in previous version (containing several models as well as script tools, organized in 3 different tool sets), it won't added to the toolboxes pan in ArcMap. When tried accessing the toolbox through ArcCatalog , the toolbox seems empty.
I then tried loading the toolbox into a total new mxd file saved with the newly installed version - again with no success.
I appreciate any help on this, thanks in advance