Error message in gwr.mixed function from R package GWmodel

Question

I am currently trying to estimate a mixed Geographically Weighted Regression (GWR) model by using the R package 'GWmodel'. It works well when I estimate a Multi-Scale GWR by using 'gwr.multiscale', but I get the following error message when I try to estimate the mixed GWR via 'gwr.mixed' function.

### Choose a bandwidth by minimizing the AICc
bw.exp.aic <- bw.gwr(mod, data=GWR.db, approach="AIC", kernel="exponential", adaptive=TRUE, dMat=dm.calib, longlat=TRUE)

class(mix.db)

[1] "SpatialPointsDataFrame"
attr(,"package")

[1] "sp"

mod

spec.imb ~ great_upsk_need + slack_rate_15_64 + ec_act_rate_F_15_64 + 
    GVA_J_share + GERD_GDP + comp_empl

fix.var1

[1] "slack_rate_15_64"    "ec_act_rate_F_15_64" "GERD_GDP" 

mix.gwr.exp <- gwr.mixed(mod, data=mix.db, bw=bw.exp.aic, kernel="exponential", fixed.vars=fix.var1, intercept.fixed=TRUE, adaptive=TRUE, dMat=dm.calib, longlat=TRUE, diagnostic=TRUE)

Errore in dimnames(x) <- dn : la lunghezza di 'dimnames' [2] non corrisponde con l'estensione dell'array`

I have already tried to set the argument intercept.fixed=FALSE and to change the vector of fixed variables, the bandwidth, and the kernel function. So, I am really not able to understand where the problem is.