I got this answer from the Strawberry people :
Unfortunately v5.12.3 doesn't handle properly upgrade so your troubles are probably due to the mix of 5.12 and 5.16 dlls which do not play well together.
1/ uninstall strawberry
2/ manually delete c:\strawberry (or what was your install directory)
3/ make clean install using 5.16 MSI
I have done what i said before, instead : uninstalled Perl, then installed v5.12.3 (the one i initially had). Everything seems to work alright, but i have to re-download and install all the CPAN modules that i use...
After that, i will try and use Pinto.
And after that, i will try and use perlall to upgrade to v5.16. What i don't know is whether i can use it to install a v5.16 Citrus Perl, along with Strawberry v5.12. It doesn't sound right to me, for some reason. I might as well start from scratch with Citrus v5.16, and hope that my code is Citrus v5.16 compatible.
I'm lucky to have this problem while my code base is still small.