It's not possible to run MESS with categorical variables because they need to have a minimum and maximum that signify low and high values. You could calculate the proportion of the land cover classes within a buffer zone around each point and use these numbers as continuous variables. I would caution against using all of them (so that summing the proportions add up to 1), because that will lead to very high correlation between two or more of them. What Maxent usually does when variables are highly correlated is choose one to do most of the explaining, but the one it chooses can be random, and so it's hard to trust the variable importance values. If you are just interested in getting an accurate prediction, this is not something to worry about too much, but if you plan on interpreting the model response curves, etc., you should make sure collinearity is not too high.