Have been running WSPR for some years on old XP machine with complete success. Decided to update and loaded WSJT-X. Seemed to be OK but will not run for more than 2 cycles. At end of second 2min cycle everything disappears off screen. If shortcut pressed to restart a block appears "Another instance is running. Purge LOCK file?". If "yes" program reappears and again runs for 2 2min cycles before switching off. Original WSPR still running OK. What's a "lock" file???