You should make sure that you have the correct driver for your phone/USB cable, the most current version of Bitpim, turn off and reboot your PC and your phone (and I would delete out the ringers from Bitpim and the phone if they apparently made trouble for you), then restart from scratch (abandoning the ringers you already made - I made some and renamed them after editing and it made trouble for us too). When you restart, make double-sure that Bitpim stays set for your phone (we have to use the settings for a VX8300 to work with our VX5300s and sometimes Bitpim wants to default back to the "other
CDMA phone" when it autodetects) and go from there. Do not modify/rename/etc the ringers you make in Bitpim (we save them to a ringer file for each specific phone type). From my experience with Bitpim, if you make a ringer for one phone (did some for our daughters enV9900 phones) and try to use them on another phone (our two VX5300s) it will not work.
I hope this helps you
Tracy