If Rezzed Items Have Vanished
Unfortunately, this type of issue is more often related to asset server problems than the problems in the "Lost Items" blog, and unlike caching and loading problems, asset server problems are often not reversible. You may notice that when Linden Lab posts grid status problems, they will often warn not to rez no-copy items during that period of time. This is why. Nonetheless, there are a few things you can try.
First, check your Lost & Found folder in your inventory for the item. The object may have been returned to you without your knowing. Check your Objects folder, as well.
Second, relog. Sometimes, this is all that is necessary for missing items to show up in your inventory again.
Third, go to point 0,0,0 in the region or, if you don't have access to it because it is part of someone else's private property, ask that parcel or region owner to look. Sometimes, rezzed items will be deposited there.
To get to point 0,0,0:
Either type “gtp 0 0 0” into local chat (without the quotes) and hit Enter;
Or open your mini-map (top menu, World → Mini-Map, or Ctrl-Shift-M) and fly or walk to the far southwest corner of the region.
Fourth, try searching for the item using Area Search:
Go to top menu, World → Area Search.
Click on the “Find” tab and type part of the name of the item into the “Name” field. Click “Search.”
You will be taken to the “List” tab. If you see the name of the object, double-click it in the list and follow the red beacon to the object.
Moving your avatar or camera around can help the Area Search detect items that are not detected initially.
Fifth, if the region belongs to you, you can ask Linden Lab to roll the region back to a point before the item disappeared.
Sixth, if you have another viewer installed, log in with it to see if the missing item shows up in your inventory there. If it does, then try the suggestions in the “If You Are Missing Items in Your Inventory” section above. If it does not show up in your inventory in either viewer, then Second Life may have lost the item.
Don't forget to check unknown "object" boxes in your inventory. SL stores multiple items returned to owner by land settings or group return and when opened, you may well find your missing items in there!