This gives information about data fetching in particular table which you mentioned in the script. After sucesful fetched this dialog box disappear because tick of close when finished at the bottom.. For every reload it checks all data fetchibg correctly or not.
I wonder if the reason it is hanging is because QlikView is creating 'synthetic keys'.
Have the tables "Dec-Mar_USD" and "Dec-Apr"_USD got the same field names in them? If so then QlikView will try to create relationships on these fields and could take quite a long time, depending on how many fields you have in common in the two tables.
Are you aware of the 'Qualify' keyword? This may help you to stop QlikView relating the fields in the two tables together and then you will be able to look at the results.
Just briefly, using Qualify on particular fields will insert the table name before the field name so for example the "Exchange Rate" field in the Currency table would become "Currency.Exchange Rate". This means that if you have another field called "Exchange Rate", because the field names are now different, QlikView will not make a relationship between the two.
I'm sure the help will probably explain it better than I have!
As you have seen though, you can fix the problem without the need to use the Qualify keyword which is great. Usually I find that using the Qualify keyword is just a temporary thing before I have fully developed my data model.
Keep exploring, I've been using QlikView for the best part of 2 and a half years and I still am!