I just installed Amibroker 6.40.4, Buildate Feb 2,2022. (x64)
I copied the data directory from another instance of AB into the c:\programfiles\amibroker directory.
Opening AB everything looks good. When I run a backtest of an existing afl file I am getting the error in the image. This AFL file works on my other instance of AB.
the symbol in question does exist and I can see all its history on the price chart.
It looks like that this error appears for each symbol the backtest tries to analyze.
The only way to stop this is to terminate the application via Task Manager