the SQL server database engine cannot obtain a lock ressource at this time

AhmedYeddes 

One difference is that 

SELECT col1, col2, [...] INTO tableA FROM tableB

Creates a new table, tableA, then performs the insert operation.

INSERT INTO tableA SELECT col1, col2, [...] FROM tableB

on the other hand, appends the selection to an existing tableA.

While I cannot verify this, I'd assume SELECT INTO puts a table lock on the table, as it's created as part of the statement, whereas INSERT INTO is attempting to use clever locking to minimize impact on SELECTs on the target table, resulting in a hot mess exhausting your resources.

As others have suggested, I'd suggest specifying WITH (TABLOCK), which will impose a table wide exclusive lock for the INSERT.

You can also get this error message if there's not enough memory resources available.