I just encountered this error.

The steps were

Begin Tran

TRUNCATE Table1

INSERT INTO Table1(Columns...)

SELECT Columns From Table1Backup

This would give the error at the INSERT statement

Changing the Truncate Table to DELETE FROM Table1 allowed the process to work. I would guess that the way Truncate works is preventing inserting into the table (due to locking?) until the Truncate has been committed.

Perhaps other situations are similar with an attempt to update or insert into a table that is locked within the transaction.

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JimFive