My new Lenovo Laptop is authorized for iTunes and i have my apple username which includes my @gmail account and my original I Tunes Password.

I have a number of purchased (i.e. paid) I tunes songs. All played routinely on my old laptop which for several years has my @gmail included in my username.

Now when I select some of those purchased songs I get an error message " do you wish to authorize this song for tis pc ? you purchased this dong using xxx@slingshot.co.nz and asks me for a password..

I have tried replacing the @slingshot.co.nz with @gmail.com and my iTunes password. -failure.
I then leave the @ slingshot line as is and enter the original iTunes password I had when I used slingshot-failure.

I then select "forgot user id password" then get a text with an authorization code-apply it but then just get "this pc is authorized" and quoting my @gmail username.

I registered with iTunes forum but ability to enter a detailed question is severely restricted.

Any ideas why on some of my purchased songs I gr confronted with this issue?

Help please.