I'm a bit confused by your explanation.

So to clarify, you are saying that if you use the coworkers wallet.dat as the ONLY wallet.dat it works OK? But if you try and use multiwallet functionality then Bitcoin Core crashes?

Or are you saying that it starts ok with "default_wallet" and "co-worker wallet.dat" files in the data directory, but when you try to switch it crashes?
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Yes HCP sorry to leave you hanging but my time was limited some of us are, Thanks locking now