1-CLICK UPGRADE - still LOADING comparison and unable to UPGRADE

[J-works.cz]

Hello,
    I am using official addon 1-CLICK UPGRADE and it is working only for the first time (first upgrade).
I was trying to upgrade in two cases:
    1) PS 1.6.0.9 -> PS 1.6.1.24
    2) PS 1.6.0.9 -> PS 1.7.5.2 [see screenshot 01]

Both attempts was successfull but after this I was about to upgrade on newest version PS 1.7.6.8 and it is not possible. When I choose any CHANNEL to upgrade (Minor release, Local archive, ..) and then click on SAVE [seen screenshot 01 - orange mark] - page is not responding - nothing is saved. So I can't choose any way to upgrade again.

On page there are LOADING BARS [see screenshot 01 - red marks] and they are still loading. The VERSION COMPARISON is still doing something.
Before first upgrade the VERSION COMPARISON was working - there was numbers with counted changes.

Does anybody know how to solve this?

I was trying to uninstall 1-CLICK UPGRADE module and install again and it is still doing the same.

THANK YOU VERY MUCH

- - - -

P.S. do you know what is the BEST PRACTICE about upgrading? Which way is the best?
ORIGINAL VERSION IS 1.6.0.9 .................................................... and FINAL VERSION IS 1.7.6.8
1) PS 1.6.0.9 ->                                                                                                                       PS 1.7.6.8
2) PS 1.6.0.9 ->                           PS 1.7.0.1 ->                                                                      PS 1.7.6.8
3) PS 1.6.0.9 ->                           PS 1.7.0.1 ->                        PS 1.7.4.4 ->                        PS 1.7.6.8
4) PS 1.6.0.9 ->                           PS 1.7.0.1 ->                        PS 1.7.4.4 -> PS 1.7.5.2 -> PS 1.7.6.8
5) PS 1.6.0.9 -> PS 1.6.1.24 -> PS 1.7.0.1 ->                        PS 1.7.4.4 -> PS 1.7.5.2 -> PS 1.7.6.8
6) PS 1.6.0.9 -> PS 1.6.1.24 ->                        PS 1.7.3.4 -> PS 1.7.4.4 ->                         PS 1.7.6.8
7) PS 1.6.0.9 -> PS 1.6.1.24 ->                                                                       PS 1.7.5.2 ->  PS 1.7.6.8