Parameter From Form Displays Garbage

Hi there!

I'm trying to use an Invoice number from an Invoice form to populate a table of Invoice Lines with relevant records (linking by Invoice number). I realise the following SQL code isn't an append query, but I've simplified it to make it easier to explain

SELECT [Forms]![fInvoices]![SPInvNumber] AS MTInvNumber, tInvoices.SPInvNumber
FROM tInvoices
WHERE (((tInvoices.SPInvNumber)=[Forms]![fInvoices]![SPInvNumber]));

The output I get for this query is something along the lines of:

MTINvNumber | SPInvNumber
쉠 | 49760

THe MTInvNumber should read the same as the SPInvNumber, but it doesn't. If you can't see the above, its some sort of weird chinese/japanese character I think!

I thought maybe it was a display error, but I tried using it in my append query, and it inserted it as garbage too. The weirdest bit is it actually regards the form information as equalling the SPINvNumber from the tInvoices table! :S

Any clues on how I get it to format correctly??? I'm very tired now so it's bound to be something simple!