HI Zravko,
If you are debugging and then trying to tun from control room it might night work. Because it's a know issue in chrome you can can not run 2 instances of chrome at the same time. Restart your server and try running either debug or from control room it will work.
I guess chrome started working better after 6.4.2 on wards so try it. I am running a process from last one year in Production without any issue in 6.4.2.
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Amlan Sahoo
RPA Consultant
Equinix
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Regards,
Amlan Sahoo