Calculate delta between values in column based on value in another column

Hi,

I have a table that look like this (Table1):

And another table that also contains of the Version column (Table2):

Since I want to use two slicers to select the VersionIDs I created two copies of Table2 - they are Table21 and Table22, and of course there is a relationship between the VersionID columns.

What I would like to do is to get for each Tag the delta between the values in the "Value" column, based on the VersionID (the user should always select two versions via two slicers in my report to get the deltas), so having selected VersionID 1 and VersionID 2 I want to display in my report a table like this:

I thought this would be a rather trivial problem, however I'm just not able to get it to work.

What I have so far is the following DAX for my measure: 

prop_delta =
var selected_verID1 = SUMMARIZE(FILTER(Table21,Table21[VersionID] IN ALLSELECTED(Table21[VersionID])),Table21[VersionID])
var selected_verID2 = SUMMARIZE(FILTER(Table22,Table22[VersionID] IN ALLSELECTED(Table22[VersionID])),Table22[VersionID])
RETURN

This gives me correctly the VersionIDs that were selected. So for the rest of my calculation I was hoping that soemthing like that should do the job:

CALCULATE(SUMX(FILTER(Table1, Table1[VersionID] =selected_verID1), Table1[Value])-SUMX(FILTER(Table1, Table1[VersionID] =selected_verID2), Table1[Value]))

However this doesn't work at all and only creates a "A table of multiple values was supllied where a single value was expected" error.

Thanks for any help!