With all the different extension upgrades all the time I find that I reguarly have problems with one extension afetr installing another, and I am always careful to only install the "newer" versions of files.
The solution seems to mostly be one of two things ...
- quit DW, empty cache, restart DW, try again
- uninstall offending product, reinstall
and sometimes ...
- uninstall and reinstall eCart, which seems to walk over everything