I have also noticed this same problem very recently. Any ideas why so many invalids all of a sudden ??

Eventually i received totally nothing

20685   2013-11-01 17:25:32   6:02:53   1402679276   78300   0.00000000   267325   25.04368520    confirmed

And that is not nice it costs me power to do those 78k shares

It gives me an unsatisfied feeling...hope this won't happen again

So do we think it's a luck issue or something else?

The difficulty is now 390928787, if we have found the block with less than 390928787 shares submitted our luck is over 100% and it depends on the pool speed in how many hours it will have those shares

Because your submitted shares over that time period are so low and you probably didn't hit any at near the end of the block.  Slush's pool makes you the most when you hit shares right before a block is found because of the way that the scoring works.  It's happened to me before, when my miner died and I didn't notice because I was at work.  Managed to reset it remotely, but the lack of submitted shares over that down time and a block getting solved means your score drops down.  I am assuming that your shares are the 14, 4, 3, and 19 numbers.  You may either want to upgrade to ASICs or, if you're usings GPUs mine litecoin or novacoin. 

I see, very interesting. This is also why it's important for us (Slush) to keep adding hashrate, yes?

Thanks for replying!

russell

That is an old number. The pool is at 270+ TH right now.

Err luck and hashrate are not related by any means.
You may be lucky to find a block while CPU mining now, or never find a block even with an ASIC