Long story short:

I moved some 0.1 BTC to a paper Wallet.

I removed my old wallet.dat and restarted bitcoin-qt to generate an empty new one.

With help of Debug Window i did "importprivkey myprivkey"

But still 0.00 BTC
My BTC are still there at the Address - tested with blockchain.info search

How do i rescan the downloaded Blockchain manually?
Is this even the Problem?
And yes, i restarted the client.

Is it possible the client misses out some transaction from time to time? (and so "forgetting" bitcoins?)