I guess that contact transfer app is not updated on Lumia..that is why this problem can come...

If you update contact trasfer app on Lumia and then try to pair with N900, it will work...you do not have to connect both phones to PC for transferring contacts from N900 to Lumia...

(I am sure that someone has posted above solution in Lumia forum). Today I bought Lumia and transferred N900 contacts to Lumia. Initially, Lumia was not pairing with N900, but after updating contact transfer app, it worked well.

I used N900 for nearly 3 years...it served me well...Bye bye N900...welcome Lumia...Lumia is awsome..

Thanks Nokia for Lumia product.