Command line is too long

Windows caps the length of a command line. The Papyrus compiler is called with one import folder per argument, so a long list of imports can hit that cap.

Since 5.9.0

Two changes make it far less likely:

• PCA's MO2 integration was removed. It used to pass every mod folder to the compiler, which is what blew past the limit in the first place. Run PCA through MO2 instead: MO2 gives it a single, already merged Data folder.
• Fallout 4 imports were reduced to the three roots the game actually uses, instead of every subfolder found under them. Refer to Papyrus namespaces.

Still hitting it

• Make sure the mo2 option is off in the settings — it does nothing but warn.
• Move the game, or your scripts, to a shorter path. Every import folder carries its full path.
• Share a debug log with us.