Likely the part you are trying to load has the same moduleId (the hex string) as a part in core parts. That is what causes the already loaded message. If someone created a new part but didn’t change the moduleId this will happen. Finding the part can be a problem though since indeed the new part may have a different name and images. Here I attempted to load a part (the fc-51) that is already in core parts which gets this message
clicking OK lets Fritzing load, and then entering FC-51 in to parts search brings up the part with that moduleId
that tells you what part in core parts is in conflict. To fix this you need to unzip the part you are trying to load and change its moduleId in the fzp file. One potential problem is the moduleId doesn’t have to contain the name of the part (as the FC-51 does) in which case you need to identify the part another way. My usual method is to use grep to search the fzp files in core parts (in fritzing/fritzing-parts/core for the moduleId and then read the .fzp file to find the part name (the title should give you the part name that will let part search pull up the conflicting part.) Not the easiest in the world but it works. Then you need to modify the part you want to load so the moduleId doesn’t conflict. This tutorial on part making may help there.
as an alternative you can upload (upload is 7th icon from the left in the reply menu) the .fzpz file to the forum for the parts that you can’t load and I can fix them up for you.
Peter