[users] Crippling extensions

[thomas steel]

Can I update my problem very precisely? I have some files with the extensions 
'.xlsm' & '.xlsm.xlsm', which refuse to open. I converted them from OOCalc ages 
ago & worked on them happily in Calc. I then shunted them into one New Folder. 
When I go to that Folder, I find these strange extensions. How can I reconvert 
them, please? T.M. Steel