To avoid this error in the future:
In rare cases, the file exists but is flagged internally as "in use" or "corrupt" even after verification. You can manually force the game launcher to rebuild it.
Type cmd into the Windows search bar, right-click , and select Run as administrator . Type chkdsk /f /r and press Enter.
Frustrating but solvable. Most players fix it with a Steam verify. A few report that Windows updates or driver rollbacks helped. Rare cases involve defective RAM or HDD sectors.
Windows file permissions can block a game launcher from accessing root-level directory items like bigfile.000 if it is installed on your primary C: drive.