Just upgraded to Windows 8.1 and it shows LogiLDA.dll error.
To stop the pop-up message coming every time you can do the following:
1)Launch the Taskmanager.
2)Under TAB Startup search for LogiLDA
3)Right-click and disable.
->Message popup resolved.
If you know Windows Registry you can do the following:
->Open Command Prompt and type Regedit
Go to: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
Find the entry Logitech Download Assistant(LDA)
Select it, right-click and Remove