Synchronisation issue on Mainnet, testnet and private network

Question

I am just unable to synchronise on any kind of network either main network , testnet and not even on private network.

I have updated my geth instance to a newer version - Geth/v1.5.9-stable-a07539fb/linux/go1.7.3.

I used the following command for the testnet as well as the mainnet - geth --fast --cache=512 console and with --testnet flag too , but kept getting the following errors -

1. Synchronisation failed: receipt download canceled (requested
2. Synchronisation failed: block body download canceled (requested)
3. Synchronisation failed: state data download canceled (requested)

And as a result when i use eth.blockNumber in the geth Javascript console, it returns 0.

Also i am facing error in syncing of a private testnet as given in this link Synchronisation issue on private network -

How can i solve the synchronisation issues ?

EDIT - I just noticed that the currentBlock value is increasing when i see the output of eth.syncing. So should eth.blockNumber returning 0 be an issue ?