unable to net send computer, but able to net send domain..help!

ok. this is a strange one.
up until a couple of weeks ago, i was able to net send
computers on my network by their computer/hostname..

for example, net send hostname1 hey! whats up..

now i cannot. it tells me that the alias cannot be found.

tho, i can net send out whole domain...
for example, net send /domain:mydomain hey! whats up!

so, i went to another computer, and was able to net send
both hostname1 and the domain fine.

tho i noticed, when i net send from that other computer,
to MY computer (that is having the issue) i cannot net
send to my hostname (it will say that a network error
occured) but if i net send the domain, i receive it.

i thought it might have something to do with my hostname,
but i can successfully VNC into my computer to my
hostname, and i can have folks sign into my FTP server
through my hostname..

seems the only thing affected is net sending to my
specific hostname or to other specific hostnames from my
computer.

to my knowledge, i have not changed a thing. the only
things i have installed are meca and easy messenger.

i do not have a firewall enabled on my LAN connection, as
our LAN is firewalled..

any suggestions as to what i should look for to start to
troubleshoot this?
please email me as well as respond..
thank you