It seems to be a problem with Adobe Flash AND SwfUpload.
The Update to Flash version 10 brought the troubles to SwfUpload.
so: short solution to get working again
If someone has an old 9er Version of Flash-Player things should work again...
but Flash 9 seems not to be available on adobes websites...
(1) Deinstall flash 10
(2) Go to Adobe Download and before downloading select 'other operating system'
(3) then select Win98 and Firefox
this will leed you to flash-9 download *ggg*...
Install and Disable check for updates of plugins in firefox
and things should be fine again...
g
Helmut