The B-Plus file transfer protocol does not support 7 bit communication lines. B-Plus, as implemented in Tera Term, does not support file transfers between two PC's. You should use the B-Plus protocol to transfer files between your PC and a BBS such as CompuServe.
For serial port connections, set the appropriate parameters in the [Setup] Serial port dialog box. Data must be 8 bit.
If file transfers fail, try to escape all control characters.
Setup item for B-Plus:
Auto activation of B-Plus Receive