"..since I don't know if I just have lost another few nano prims somewhere in my shop or on my sim."
I hate that feeling. I get it a lot when I'm working with small objects in a really big area. SL doesn't always rez objects where I point - I had a square of grass floating in the sky at the edge of my parcel that I was hunting for days for.
I just got the "Attempt to rez an object failed" message today. I tried to attach a flight boost HUD that I wear all the time but nothing happened for the longest time. I could see by my activity monitor in the corner that SL was sporadically sending and receiving info but when it finally did something, it was only to show that error.
I cleared my cache and logged off, waited a minute, then logged back on. The HUD went on without a problem. So try that if you haven't already?