Andras,
The problem with your model is that you have a TableCurrent that is hooked up only on one side and a voltage sensor that is only connected on one side. The other side must reference a voltage (such as ground).
I added a ground and this model builds (although you could equally connect to the existing ground although the wires become messy).

As to your second question, you should change the tableCurrent to a CombiTable and a current source. CombiTable can load from various files (including ASCII and .Mat) you can easily change your .xls format into a compatible file. See the Help for the file details.
The model would look like this:

Regards,
Neil