I just installed the 2.10 version and the shadow4 widgets and the weather doesn't work.

Can you tell what exactly happened when you installed the addon and enabled the weather window?

Absolutely yes.
I install the 2.10 version of rainlendar.
The installer demands me to close rainlendar so I close.
I open the rainlendar and I see that the weather widget and text file dissapear.
I download anf install the widget from here: www.rainlendar.net/download/b110/Shadow4-Widgets.r2skin-addon
Now I see the text file widget and works perfect (now is Case sensitive (: ) and the weather widget which only shows the updating... message.
I check the URL and it's the same I have got before, but never get the info.
The url I have now is that (I think is the default url):
weather.msn.com/RSS.aspx?wealocations=wc:32669%26weadegreetype=C

I also try to install the Gweather but doesn't appear on the options.

I have the exact same problem and also it seems my event calendar is now corrupted.
(I use google weather for my weather info)
Here's a couple of errors I found in my log....

I also noticed that after opening another Rainlendar window, I suddenly have a weather city and current temp, but nothing for the Hi/Lo daily forcast.

Here's a couple of errors I found in my log....

07:17:03: [0:00:04.500] ERROR: Script download callback failed: [string "scripts/weather.lua"]:157: attempt to call field 'gfind' (a nil value)

07:17:04: Error: Failed to open 'F:\PortableApps\Rainlendar2\Glenn's Events.ics' for reading (error 21: the device is not ready.)

07:17:04: Error: Failed to retrieve file times for 'F:\PortableApps\Rainlendar2\Glenn's Events.ics' (error 21: the device is not ready.)

The 2 "Events.ics" errors repeat themselves several times in the log.

Got my events.ics to work by importing it again. We'll see what else I come up with.

About the widget of weather, Rainy wrote (in b119):
Some of the scripts got broken by the Lua 5.2 update.
I replaced the old weather widget in the Shadow4 addon with the GWeather.
The download link is :
www.rainlendar.net/download/b119/Shadow4-Widgets.r2skin-addon

Added:
I found a bug that the refresh time is always at 1970-01-01 00:00:00 +0000 (see image)