Error 3048. "Can't open any more databases."

Has anybody experienced this error?

Using Microsoft Access 97.

I get it when I am adding objects to a collection (the objects may contain other collections too). I am not opening databases. Once it has occurred I have to reset to clear it. Before resetting if I try to open a table I get 'Can't open any more tables'. Presumably I am running up against some limit but I can find no mention of limits in the Microsoft knowledgebase.