Hi and welcome to the forum
A miscompare during the verification step means that the contents on CD are not the same on the HDD.
Causes can be mainly two: something went wrong during the burn (most of times the cause is a defect on CD disc), so the CD should be burned again, or you have problems in computer RAM. Also a damaged cable can cause problems.
To check RAM you can use memtest (it's a really easy, but a bit time consuming, test to perform).
btw, even if there is a miscompare the CD can still work correctly (I'm assuming that you are referring to an audio CD).
If you are referring to a data CD, then a miscompare can cause serious problems. For example, if the wrong data are located on a RAR file (even worst an archive containing a password), the wrong file can be unrecoverable, so it is definitely better to burn again that CD after checking that there are no problems in RAM.