Error
Value cannot be null. Parameter name: InString.
Cause
This error indicates that an item failed to migrate because it has corrupt MAPI properties. More specifically, Exchange Web Services (EWS) returned a MAPI property whose value should always be a non-empty string but was returned as an empty string.
This may affect calendar items that do not show up in the user's calendar. Because those items are detected as corrupt by Exchange, OWA (for example) will not render them. The API still returns the offending items, so we report an error.
Resolution
We recommend the following:
- Identify the folder(s) the failed items came from (for example, calendar folder).
- Ignore the error. The item is corrupt and cannot be migrated.
- Consider filtering the folder. A folder may contain many corrupt items.
- Consider specifying a date range. A folder may contain old items incorrectly upgraded from a previous version of Exchange.