[j-nsp] ERX - Problem upgrading from 5.1.1 to newer release

[Rolf Frøysa]

I`ve tried upgrading an ERX from 5.1.1 release to a newer release but I 
end up with the following error:

ERROR os: Boot configuration too long for this platform.  Discarding change.

After doing some research I found that I require release 5.1.2 or newer 
5 release to upgrade to a higher release.

ref. 
http://www.juniper.net/techpubs/hardware/erx/frus/srp-flash-sw-upgrade.pdf

After checking on the juniper pages, I see that all 5 releases are 
unsupported and removed from the archives.

As far as I can understand, they did some changes to the bootprom or something in the older 5.1.2 or newer 5 release to increase the accepted size of the future releases? Is there any way I can fix this issue without having the 5.1.2 or newer 5 release?

-- 
Sincerly

Rolf Frøysa
Cell +47 90 59 45 91