These three codes are frequently reported together in QBWin.log. They each represent validation failures at slightly different points in QB's data verification routine — C=21 typically fires during record-level field validation, C=73 during cross-record reference validation, and C=179 during higher-level structural validation. When all three appear together, it usually indicates a single record that is failing validation at multiple levels — the fix is the same for all three: update QB, then Rebuild. If they persist after Rebuild: identify the named record from QBWin.log → resave it → if still failing, delete and re-enter.

Field Value Validation Failure

Primary C=21 cause — a record's field contains a value outside its valid range or of an unexpected type. This could be a date field containing an invalid date, an amount field with a value that doesn't match expected decimal precision, or an account code that doesn't conform to QB's format rules.

Interrupted Record Save

A record was partially saved during a crash or power failure — the saved partial record has fields that individually appear valid but collectively fail QB's cross-field validation rules. C=21 flags the field-level failure while companion codes (C=73, C=179) flag other validation levels on the same record.

Data Imported with Non-Standard Field Values

Data imported from another accounting system or third-party app may have field values that are acceptable in that system but fail QB's stricter field validation rules. C=21 appears when Verify runs its field-level checks on these imported records.

Version-Specific Validation Bug

Some QB releases have overly strict validation rules that flag valid data as C=21. Updating QB to the latest point release often resolves false-positive C=21 errors that a previous version's validator was reporting incorrectly.

Disk Corruption

Bad sectors or file system errors modified stored field values after they were written — the modified values now fail field validation. Run chkdsk /f on the drive hosting the company file before attempting repair.

General Company File Corruption

Broader file corruption affecting multiple records can cause C=21 errors across many Verify Targets simultaneously. Multiple C=21 entries in QBWin.log for different record types suggests widespread damage rather than an isolated record issue.