"Out Of Memory" error in excel VBA for a very large model. How can I avoid this?

I am trying a declare a new variable in VBA for Excel. I have an excel model which has 9 modules and 7 class modules. Each module is really large, with an average of 60 variables declared in each module and a minimum of a few hundred lines of code to a maximum of a couple of thousand lines of code in each module. Every time I try typing a new variable, I get an error that says "Out Of Memory". How can I avoid this error and continue declaring more variables ?