Login failed for user 'nt authority anonymous logon'

Hi All,

we are in progress of changing our windows services from sql account to windows authentication.
So conn string will be changed to "data source=XXX ; initial catalog: XXX ; integrated security=true"

for one of the services, it is working but for another it generates error
login failed for user 'nt authority anonymous logon'
i have tried with integrated security=SSPI, still same error.

No idea what is the reason, the one it is not working is c# console application.

Thanks.
techie