Whats probably the cause of the SL Release viewer-4.0.3.312816, not "completing" logins

[ral61]

The "new" SL Release viewer-4.0.3.312816 is completing login's, past the region handshake to the Secondlife Grid.

I tried "clearing" cache files, but that only login the viewer a "few" times, before login issues appear to happen again, 

with a (stable) internet connection. This is suggesting SL has to upgrade to another version rather "quickly",

for completing logins constantly.

[Rolig Loon]

Clearing cache is generally a bad idea.  It doesn't solve very many problems and it can actually make some things worse.  Don't do it unless you have a good reason. 

If your viewer is stalling when it gets to the stage of getting a "region handshake", the reason is usually that your firewall or an overly aggressive anti-virus routine is blocking your access to the SL servers.  See

https://community.secondlife.com/t5/English-Knowledge-Base/Using-Second-Life-with-a-firewall/ta-p/1304539

 and

http://wiki.phoenixviewer.com/antivirus_whitelisting

You might also try rebooting both your router and your modem to get a more reliable Internet connection.