Without more information its difficult to tell exactly what is going on, but I can make an educated guess: It likely means that the person that created that model didn't export it correctly and it uses inches as its size unit rather than mm (which is what slicers expect).  To fix that you would want to scale it (in all directions) up by exactly 2540%. (This essentially converts inches to mm)

Do not scale to fit, thats just going to make the model scale up to be the size of your build area, its not actually going to fix the problem in a way that will allow you to get the part to be the exact size that it should be.

I do have the same problem with a small model. Other slicers as well as blender can open the exported model without any issue. I can send the model if that helps you debugging the problem. This is forcing me to use another slicer.

Just use the "scale to fit" function to rescale the .stl model and if desired the other sizing tools to make it the size you want. Other slicers that "load it OK" are ignoring the scaling factor in the file, rescaling the model, and just not telling you about it.

You will see a similar "warning" (actually an "alert") from Chitubox if the .stl file scaling factor is too large.

@Cliff Knight - I think what you say the other slicers do is highly annoying and would drive users mad... I intend to use my parts for functional and not for decoration purposes so the size is the most important thing and I'm pretty much forced to use another slicer, so I'll test print using another slicer and let you know if that's the case. From the 3D Viz and the measurng function of Lychee for example, it seemed the parts were the correct size.

I oversimplified my above answer, in fact .STL files are "unit-less", dimensions are calculated by the vectors of the mesh's triangles but no unit of measure is assigned--a dimension of 1 is just 1 "something".  It's up to the rendering software to assign/assume a unit of measure. Each product can do that differently, but most seem to assume an .stl dimension of 1 = 1 mm (as does Chitubox). If the system that created the file had some other notion it will be displayed larger or smaller by Chitubox.

As an example, here's a front towing eye bar for my side-by-side I designed in FreeCAD--it is 11" long. FreeCAD built the .stl file assuming it's was sized in mm (the unit of measure selected in FreeCAD's "Preferences..." options is for display and input purposes only; it still "thinks" in mm):



So, when imported into Chitubox it is considered too large, assumed by CB to be 279.4 mm long (11 * 25.4):

Next, my scaling it by 39.37%  (should be a familiar number) results in Chitubox declaring it to be 11 cm long

2.54 cm = 1"; 2.54⁻¹ = .3937

Printing this produces a perfectly proportioned 11 cm long (1:2.54 scale) )model. I.e. re-scaling in CB or any other software does not introcuce any negative concerns--it just changes the size of the finished piece; quite evenly and proportionally...
 

No one here probably cares, nonetheless here's the final product:


painted & mounted: