there are some warning like this one Warning: Can’t find file ‘/Game/2DSideScrollerBP/2DSideScrollerOverview’
or this 
Warning Warning Unable to generate long package name for …/…/…/…/…/…/Users/ /Desktop/demo finale/Content/Maps/Untitled.umap because FilenameToLongPackageName failed to convert ‘…/…/…/…/…/…/Users/ /Desktop/demo finale/Content/Maps/Untitled.umap’. Attempt result was ‘…/…/…/…/…/…/Users/ /Desktop/demo finale/Content/Maps/Untitled’, but the path contains illegal characters ‘.’
take a look at them. probably the location of those assets which are mentioned in those warnings have been changed or they are removed.