The flashcard module was originally written by Valery for 1.9. It was hosted on the old Moodle plugins database, there was also an version initially ported to Moodle 2.
Tomek took over the work on it, finished porting into Moodle 2 and done few releases on the new plugins database page (this one). The latest version of this module is 3.2 and is available on github: https://github.com/tmuras/Moodle-Flashcard . It includes set of fixes from that should get it to work on Moodle 2.5. You can use it but this development is dis-continued.
Valery has now updated his branch of flashcard module into Moodle 2.5. The source code is https://github.com/vfremaux/moodle-mod_flashcard and the latest release is also on this, new plugins database as 2.4.0 (Build 2012040100). This is the branch you should be using now.
Both versions of flashcard module have diverged and are not compatible with each other. It's not possible to easily switch from one version (3.1 or 3.2) to another (2.4.0) without re-installing (and hence loosing all data).