Hi mpfitex,
I'll try to explain that the best that I can (english isn't my native language, so...) but first a brief summary of what's going on with WPP 2.0:
The _popularpostsdatacache is a new addition in 2.0. That table did not exist on any previous versions of my plugin. That's why it's empty, but it should start filling with data as soon as your visitors check your pages.
Now, what does _popularpostsdatacache do? It's purpose is to store all views in the last 30 days from the current date, after that the plugin will wipe out all registries that have been in that table for more than 30 days to avoid making the table too large. When someone visits any page of your post, my plugin will register that in both _popularpostsdatacache and _popularpostsdata ("cache" and "data" from now on).
On the other hand, the data table will store all info about all those posts that have been in cache (some sort of a historical table). These entries will not be deleted automatically by my plugin (unless you wipe it out via wp-admin > Settings > WordPress Popular Posts).
When you set Time Range to "daily", my plugin will look for all records in the cache table and select those that have been viewed today. Something similar will happen if you select "weekly", or "monthly": the listing will be build from the information stored in the cache table. However, setting it to "all", will make my plugin switch to the data table (_popularpostsdata) and extract all the info from there (that's where are stored the recordings from version 1.5.1).
If you have set Time Range to "daily" now, WPP will look into _popularpostsdatacache and there's no information there yet - that table needs to be populated. That's why you're getting the "Sorry, no data so far" message.
Allow me to suggest you to switch Time Range to "all" for a while (a couple of days would be enough if you want Time Range set to "daily") so that the cache table is filled with data as your visitors check your pages.
A long explanation, I know, but I wanted to make it clear enough for others who might read this thread ;)