When you see a size mismatch like this, three possible explanations come to mind
- something is wrong with the size of the data in the inputs
- the variables are being computed incorrectly
- the variables and computations are fine but the line of code is not correct
Where I would start troubleshooting depends on context. If lots of others have used this code without problems and it comes from a reputable source, I'd start with #1, assuming I screwed up the inputs.
If I wrote the code yesterday after losing sleep for 3 days and was suspicious that gnomes may have messed with my code, I'd start with #3 after checking that the inputs make sense.
If you confirmed that the code is not the problem and your inputs are correct, then start with #2.
