Reinstalled Ubuntu three times
Problems with fTools, as I mentioned before, on Ubuntu Karmic with QGIS 1.4.0 were "solved" (as I`m not very trustworthy to freeware)
Firstly I followed these instructions, installing and compiling ECW, MrSID, GDAL and GRASS seperately from QGIS, but still while making fTools "Dissolve", QGIS crashed.
Launching QGIS, on terminal I got an error
*** glibc detected *** qgis: double free or corruption (fasttop): 0x00007ff38002b9a0 ***
and I found out, that this glibc error is solved by typing