Warning: Connection timeout. Retrying... in Vagrant

I got this error when trying to ssh connect to Vagrant instance.

slave01: SSH auth method: private key
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying...
    slave01: Warning: Connection timeout. Retrying…

This is how I resolved that.

Check the running VMs using the command below:
vboxmanage list runningvms

"Cluster_master_1425452823416_28694" {5b4505cb-2b48-45c1-a941-8e4b2d36f29b}
"Cluster_slave01_1425452852606_67792" {740aa005-6666-43e0-9631-a2f2d6e4caa5}
"Cluster_slave02_1425452882392_41607" {888cf959-1978-4474-86ef-ddfaaf3491f5}

Provide the required keyboard input (enter in this case) using following command:
vboxmanage controlvm Cluster_slave01_1425452852606_67792 keyboardputscancode 1c