It sounds like you are reading the data incorrectly, for example, you have blanks in a free format data set. If you cannot figure it out, send the files and your license number to firstname.lastname@example.org.
Thanks for your reply. I am currently waiting for my license information from UVM (I use university computers because I have a Mac). I think I found the problem. My data was exported from limesurvey and was set to have 11 columns in each variable. Do you think that would cause the issue? Are there any help guides on importing data into MPlus from SPSS?
The number of columns in the data set must correspond to the variable names on the NAMES list for the data to be read correctly. You should see the SPSS manual to see how to convert an SPSS file to an ASCII file.