webx.db is the Web Crossing Database file. This file is nearly always being updated. Interrupting Web Crossing without a proper graceful shutdown can corrupt the database.
For example, but not limited to:
Power Failure.
Hardware problems...most typically flakey disk drives, sometimes bad memory modules..same as with any software.
Forcing Web Crossing to shut down improperly (kill -9 rather than make-quit).
Web Crossing dies due to other system process(es) crashing and taking WebX with them.
A reboot without prior proper WebX shutdown (assuming your system doesn't try to shut webx down normally by default).
Multiple instances of WebX attempting to access the same database.
Insufficient available sytem memory or disk space or heavy virtual memory "thrashing".
Extremely low cache settings for a large and/or very active database ("Memory Usage").
Restoring webx.db directly from a system backup and not via Web Crossing generated backup files (webxdb.NN and webxroll.NN).