"An attempt was made to load a program with an incorrect format" thrown in debug but not from unit test. Why?

Hi I have looked at other answers and I don't see anything that would answer this, I have code that executes correctly when initiated by a unit test but throws

An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)

When the same method is called with the same values in debug mode the line that throws the error :

dbConnection = new SQLiteConnection(@"Data Source = " + pathtoDB + "; version=3;");

In both cases where it is called there is no difference in pathtoDB, as I say my unit test has no problem with this method but debug fails. I have no idea why.

Edit - Thanks for the links, but it's not actually answering the question, I accept that it's possible that the dll for SQLite may not be x64 but that does not explain why this runs correctly from a unit test but not from a debug session with exactly the same parameters. It is this that I am seeking an answer to. I have also updated the title

Edit - The Sqlite stuff is x64 it's not that that is causing it, just an update it's not changing the question.

With reference to [Dave M] who has explained the reason, this is closing off the question with the steps to rectify the issue.

To correct the problem, the [Solution Properties] was opened (VS2017) - an additional configuration was created from the [Configuration manager] with the platform set to x86 for the Project and Unit tests.

The solution was run in Debug and successfully completed the connection to the Database.