I get this error when I try to optimise the model. Everything up until this point works perfectly but for some reason Xpress refuses to recognise my constraints as being constraints and gives me a message "Error E-1101 - Empty Problem"

I've looked up the error in the reference manual it says - "We are trying to generate or load an empty problem into a solver (*i.e.* no constraints; bounds do not count as constraints)". I've tried specifically defining the constraints instead of just using them (as every model that works fine, including my own, seem to do). I've reduced the model to include only the simplest constraints that appear no different from any other working model but it doesn't change anything.

The only thing I thought it might be is the fact that I'm using the record data structure which I haven't used before however if this in included with Xpress surely there's no reason I can't use it? Plus, as stated above everything up until the "minimize" function works fine.

Help please!

It looks like some data structures (I am thinking in particular of dynamic arrays of decision variables that require an explicit "create") may not have been initialized. Could you share some more detail about how you state your constraints?

You could also try to visualize the size of arrays to check whether they have the expected contents.