TCP won't Recover..

A customer of mine has TCP/IP running, supporting Network Stations...
For some
strange reason, at different times, communications to host is lost... NO
errors
on qsysopr or any were else.... I have tried in this order:

1. endtcp
2. endhostsvr
3. endsbs qserver

I then :

1. STRTCP
2. STRSBS QSERVER
3. STRHOSTSVR *ALL

We still can not get the network stations to connect to host....
we get errors such as: Searching for Host
                       Host System cannot be contacted
                       
What appears to happen, is that it finds bootp on 400 but when login
is attempted, it fails.....
This system has been running with net stations for over 3 months.. but
this situation comes up maybe weekly and I have NO idea why.... The
only way it gets fixed, is with an IPL which can't be right.....

ANY IDEAS...... running V3R7 with current PTF's......
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