There are hard links instead of relative links in the .uvproj files for some of the STM32 demos which make them not compile out of the box.
ChibiOS-RT\demos\ARMCM3-STM32F100-DISCOVERY\keil\ch.uvproj
ChibiOS-RT\demos\ARMCM3-STM32F103\keil\ch.uvproj
ChibiOS-RT\demos\ARMCM3-STM32F107\keil\ch.uvproj
For example, line 412 of the project file contains
D:\Progetti\ChibiOS-RT\os\ports\RVCT\ARMCMx\STM32F1xx\vectors.s
and it should be:
......\os\ports\RVCT\ARMCMx\STM32F1xx\vectors.s
Thanks for finding.
Will be fixed in 2.6.1stable, 2.7.0unstable, fixed in repository.