Yes it cause problems! you have to use the same version for example APAC FW need APAC FS and custom files you can't use GENERIC FW if you want to do that you have to flash GENERIC FS too
NOTE:FW it is the Firmwae and FS it is the File systems all ringtones pictures and stuffs are located in fs and main programs in FW
I had that problem with one of my friend's phone you have to flash it manually by using XS++ or Setool2lite
and for firmware here in topsony only you can find W800 FW and FS in CID36 not CID49 you have to check you phone CID first by XS++ or Setool2lite then ...