One mate is coincident. the other is a distance.
I need to add another distance dimension to have the parts in the correct location.
I am a 22 year veteran of Solid Edge.
I have stumbled through SolidWorks and find that it is not as good as Solid Edge.
I frequently have this over defined error in assembly and the parts and not even close to being located properly.
This is very frustrating.
My guess would be that you're trying to mate another face and if the component is an imported file from another extension there is a chance that the surfaces aren't exactly parallel/perpendicular. Delete the mates you have and find three points and mate those coincident and if they take then your surfaces have an issue...
Michael what John said above and one other note. On most custom extrusion profiles there are variances of minor angle changes out to 4 or 5 decimal places that solidworks will burp out you cannot make them parallel.
We deal in window and door seals and see this frequently on extruded profiles especially scaled ones for pull die work where there are 2 surfaces on a profile that look parallel but are actually out by minor fractions of a degree.
The shapes were all created in SolidWorks, not imported.
I have gone to great lengths to make sure the lines in the part drawings are defined.
It seems that you have to work really hard for this program.
The program should be doing the work for us.
When I first started using SolidWorks I got those errors all the time, and you're right. They can be frustrating. I still get them occasionally. I've found that when I get them there's almost always a problem with what I'm trying to do. Is it possible that two edges that should be perpendicular aren't, or something similar? Can you Pack and Go the Assembly to a zip folder and post it here?
Something that has helped me a lot for mating is researching GD&T reference frame, and the minimum needed to define a point, a line, and a face.
You know you can 'lock' a part's movement with only 6 points? 3 points to define a bottom plane, 2 points to define a face perpendicular to the first face, then just one point to lock in a plane perpendicular to the other two planes. Keeping that and other things I learned from GD&T in mind as I mate parts together really helps me, and I've had to work on assemblies that are made to change on the fly as it runs through programs like DriveWorks.
It looks like one part is fixed and you have added a mate to the fixed part. Can't be positive on what the 2 mates are.