[R] Solving “unused arguments (length = 4, lambda = 0.5)” error in kernlab

I recently got this puzzling error from the kernlab package, in a script that used to work really nice before:

Error in laplacedot(length = 4, lambda = 0.5) : 
  unused arguments (length = 4, lambda = 0.5)

Switching method didn’t help, for instance with a radial basis kernel instead of the laplacian one:

Error in rbfdot(length = 4, lambda = 0.5) : 
  unused arguments (length = 4, lambda = 0.5)

Apparently someone asked that on Inside-R and Stackoverflow, but didn’t care to share their solution beyond “I figured out that it’s all because of the format xtrain and ytrain”.

Well I eventually figured that out too, it turns out xtrain must be a matrix, so the fix is as simple as changing this:
svm.kernlab.mdl = ksvm(Xtrain, as.factor(ytrain),kernel="laplacedot");
into this:
svm.kernlab.mdl = ksvm(as.matrix(Xtrain), as.factor(ytrain),kernel="laplacedot");
Of course, package maintainers could do the conversion themselves, or at least provide meaningful error messages…

I use this code in a classifier wrapper in R package mc-r, currently under development and accessible at Google Code and Bitbucket:
https://code.google.com/p/mc-r/
https://bitbucket.org/patheticcockroach/mc-r/src