Too begin with, Make Terrain is not a Advanced Terrain function. DarkBasic Open Source Version, added some dll's and moved some of the functions around. It is my guess that the residual dll's are causing conflict. These snippets reflect what should be in your plugin folders and keyword folder, based on DBPro Version 7.4. Try deleting any other files found in these folder, unless you have installed a third party plugin your aware of. If you don't have one of these files, it just means the update you installed over the open source version is older then version 7.4. Hopefully this will work.
Plugins:
plugings
--------
compress.dll
Conv3DS.dll
ConvMD2.dll
ConvMD3.dll
ConvMDL.dll
ConvX.dll
DBProAnimationDebug.dll
DBProBasic2DDebug.dll
DBProBasic3DDebug.dll
DBProBitmapDebug.dll
DBProBSPCompilerDebug.dll
DBProCameraDebug.dll
DBProCore.dll
DBProFileDebug.dll
DBProFTPDebug.dll
DBProImageDebug.dll
DBProInputDebug.dll
DBProLightDebug.dll
DBProLODTerrainDebug.dll
DBProMatrixDebug.dll
DBProMemblocksDebug.dll
DBProMultiplayerDebug.dll
DBProMusicDebug.dll
DBProOwnBSPDebug.dll
DBProParticlesDebug.dll
DBProQ2BSPDebug.dll
DBProSetupDebug.dll
DBProSoundDebug.dll
DBProSpritesDebug.dll
DBProSystemDebug.dll
DBProTextDebug.dll
DBProVectorsDebug.dll
DBProWorld3DDebug.dll
icon.ico
rawcursor.cur
rawicon.ico
workcursor0.cur
plugins-licensed
----------------
AdvancedTerrain.dll
AdvancedTerrainExpansionPack.loc
DBProGameFX.dll
PhysicsMain_PC_Master.dll
PhysicsMainLang_PC.loc
plugins-user
------------
DBProMultiplayerPlusDebug.dll
DBProODEDebug.dll
ShaderData.dll
Keywords:
Keywords100.ini
keywords105.ini
keywords107.ini
keywordsAT.ini
keywordsMP.ini
keywordsODE.ini
Physics.ini
ShaderData.ini