-openSession is only used for opening [sessionname].xml files that were saved with file > save session

a saved session file is not a document itself, but a list of tabs/files that were opened, when you saved this “session” to a file.

the correct way to open notepad++ and one specific file is:
"path_to_your\notepad++.exe" "c:\my databases\aviation\txt\CurrentLog.txt"

i don’t know your database app syntax for opening a program plus one argument value, but looking at your template it could be something like:
sys_shell_wait("path_to_your\notepad++.exe", "c:\my databases\aviation\txt\CurrentLog.txt",.T.)
although i don’t know what the ,.T. would stand for.

or if only one command without additional argv’s is allowed, you might need to “escape” double quotes in double quotes with a \:
sys_shell_wait("\"path_to_your\notepad++.exe\" \"c:\my databases\aviation\txt\CurrentLog.txt\"",.T.)