"Could not find installable ISAM" is a Jet 4.0 exception, so we know that part works.

I'd guess that you just have a poorly formed connection string. Try something more like:

Code:
"Provider='Microsoft.Jet.OleDb.4.0';DataSource='C:\Data\TestDb.mdb'"
ADO can accept quotes (") or apostrophes (') as delimiters when it parses a connection string into a series of key/value pairs. Once it has seen (or guessed) the Provider and other keys that belong to it, it can pass the rest of the list of pairs to that Provider to process.

The reason to "quote" values is that some characters (such as semicolons and spaces) will impact the parsing.

You don't appear to be using ADO but something that sort of "apes" ADO, but it may have its own parsing rules to deal with. For example perhaps it doesn't accept apostrophes and requires only quotes or something. For all I know it might also break tokens at "" characters.

But looking at the docs for this class it does appear that the intent was indeed to ape ADO with only a few minor exceptions.