I believe your problem is related to what I've encountered. This VBScript creates an Access 97 MDB file
  • Set a = CreateObject("ADOX.Catalog")
    a.Create "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=test.mdb;Jet OLEDB:Engine Type=4;"
    Set a = Nothing
The "Create" method makes a locked "test.mdb" file, that becomes unlocked once the object is released. After the code runs, you can do whatever you want with the newely created "test.mdb".

I "converted" this code to a mIRC script...
  • .comopen a ADOX.Catalog
    !.echo -q $com(a,Create,3,bstr,Provider=Microsoft.Jet.OLEDB.4.0;Data Source=test.mdb;Jet OLEDB:Engine Type=4;)
    .comclose a
and surprisingly, "test.mdb" is still locked after the script finishes, and can't be removed until mIRC is restarted.

Maybe /comclose is broken.