I too am finding issues with Factions Beta 1.7.5 with Tekkit, no other mods installed. When I try typing a faction command, such as f create nothing happens and the chat returns the following string:
20.09 19:51:07 [server] INFO [Factions v1.7.5_dev] Reset faction data (invalid faction) for player awesomeo_5000
20.09 19:51:07 [server] WARNING [Factions v1.7.5_dev] Non existing factionId 0 requested! Issuing cleaning!
Can't seem to find a cause for it all...