Sketch failed to transfer to UNO but not to ETHERNET

Hi all,

I extended my existing Pachube (now Xively) upload sketch to log as well locally at a SD Card.
Now the sketch size is 31.156 Bytes.
I have here one Arduino ETHERNET, one Arduino UNO and one Arduino UNO R2.
All of them theoretical allow 32.256 Bytes, so the sketch should fit.
But only the ETHERNET accepts it. For the UNOs I got the following error message:

Binäre Sketchgröße: 31.156 Bytes (von einem Maximum von 32.256 Bytes)
avrdude: stk500_recv(): programmer is not responding

The LEDs (TX/RX) start blinking and than suddenly stop.
Would be nice to know the reason for this behaviour?

By the way, the UNOs itself do work fine with other sketches.
The used Adtuino IDE is 1.0.5 at Mac OSX 10.8.5