You do not strictly need it.
Does the TC or Airport have all SMB type names.. short, no spaces and pure alphanumeric?
Have you setup workgroup correctly..generally WORKGROUP?
It helps to turn on the guest account.
Then in windows explorer simply type.
\\TCname or \\TCipaddress
Where TCname stands for the name of the TC or AE with external drive.. or TCipaddress is just the address in normal format. eg by default, 10.0.1.1
If it refuses to open..
In a windows command type ping TCname or TCipaddress
If that fails that is why the agent is not starting.. it has no connection to the TC and doesn't know there is any device.