This error is caused when two assets of the same asset type (e.g., two items) use the same short ID. The error will appear in the Client.log and the in-game "Error Logs" menu for Steam Workshop content.
If this error is occurring because of a conflict between two of the mods that you have downloaded, you should try contacting the mod author to see if they would be willing to change the short IDs that they use. Otherwise, you may need to uninstall one of the two mods due to this mod conflict.
If you created one of the two assets affected by this error, you can fix the issue by changing one of the two short IDs to a different number that is not already being used as the ID number by another asset. The two assets affected by this error are mentioned at the start and the end of the error message.
Example issue
(ItemCloud) Glider_Black [1806]: short ID is already taken by (ItemPants) Frost_Overalls_Farmer [1806]!In the above example, we see that an item with the filename "Glider_Black" is using the same short ID as an item with the filename "Frost_Overalls_Farmer".
By changing the short ID of the Frost_Overalls_Farmer to "1824", these two assets would now have different short IDs.