When opening a file created with ROOT v6.18/04 (LCG_96bpython3) using ROOT v6.22/00 (LCG_98python3) we get the following print-out:
ReadStreamerInfo, class:string, illegal uid=-2
Should we be worried by that? Note that we seem to be able to read this file just fine.
I think the same happens with 6.20 in LCG97.
ROOT Version: v6.22/00
Platform: Linux (CentOS 7) (LCG98)