The source code for the RLARM libs can be got by editting the link you were given, changing the 0 to a 1. (eg 4.20 to 4.21)
Enter your PIC/LIC and down load the source code.
New version broke my projects requires a change of fileconfig.c to fix
Source files havent been updated from 4.2 to 4.21 in comments though, so make sure you have a back up of previous versions.
What linker errors were you getting after you updated to 4.21?
You can always download older versions of the tools at http://www.keil.com/update/rvmdk.asp
That way you do not have to mess with changing URLs. As long as you had support when those versions of the tools came out, you should be able to download anything on there.
The error was related to not being able to find a #define used in the FS code.
The link is fine for the tool and IDE but versions later than I think 4.14 of RL ARM lib, I had to sign a NDA with ARM to get hold of the source code. Otherwise I belive its just precompiled Libs.
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