I am not very good at speaking/writing English and I am sorry if there is a pre-existing post covering what i am gonna explain below, if so just close the topic.
I have noticed that many people have problems each time a new sc patch is released with watching older replays. Most often the problem is not that they dont know they need the corresponding older version of starcraft to watch the .rep without bugging, but instead they seem to get discomfortable with the way to 'downgrade' sc.
An easy alternative instead of patching the game everytime you choose to switch between watching older reps/playing b.net/playing an older version of sc on hamachi is to get some old executables (those are the starcraft.exe files) and just launch the right one instaed of your up-to-date starcraft.exe. (this can be done very easily by renaming each old starcraft.exe since the game doesnt care how its instance`s exe was called).
Next thing: to watch replays comfortably from ANY folder on your disk i recommend you to get ReXplorer which is kinda out-of-date but still does the tricks with a little help (the main outdated aspect is the automatic replay version recognition since it hasnt been updated after 1.14 if i remember correctly)
TO GET TO THE JUICY STUFF: if you have the old renamed executables in your starcraft folder you can choose which one to launch in chaos launcher which enables version independent plugins (like WMODE) on older versions too. after launching starcraft via chaos just alt-tab out of the game select your rep on disk (in any folder again) right-click on it, 'launch replay in starcraft'->'starcraft' and you are good to go. Additional benefits are you can extract the map from the replays via same context menu too.
And if a new patch comes out: just copy/paste the 'starcraft.exe' to a new file like 'starcraft1161.exe' and you wont have problems continuing with this setup.
Links to the programs I mentioned above:
Old Executables (the original files from 1.04 to 1.13) are available at BW Programmers(EDIT bwprogrammers isnt hosting their old_execs package anymore it seems, for the time being just use the link below)
A newer RAR package by me containing the files up to 1.16 is available here:
Media Fire (EDIT to clear things up: this link contains all the executables i could get from 1.04 to 1.16)
if someone has problems with this download site and recommends another no-need-to-register upload host ill try to add them there too, just tell me
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ReXplorer is also downloadable at BW Programmers
Copied Description from BW Programmers: IMPORTANT : before installing ReXplorer, make sure you have installed Microsoft's C++ Runtime Library. If you don't, ReXplorer won't be able to install.
Chaos Launcher at Master of Chaos' Site
(i recommend you to get both the 1.153 and 1.16 versions until 1.161 or 1.17 comes out. thats mainly cuz most plugins are version-dependent)
hope that helps ppl to setup an easy to manage system of ever being able to watch replays independent of version (but remember you SHOULD KNOW which version the file is, but if its older then 1.14 rexplorer will be able to help, else its your responsibility)
mods may feel free to edit my post for better reading, since all that matters is the information in here.
gl hf, hope it helps to reduce the amount of ppl whining over corrupted replays everytime a new patch comes out