Using symbolic solve in matlab, won't execute inside a function I call

Basically, I run some code, I call a function and in that function I declare symbolic variables and use the solve command in MATLAB. It gives the following error:

??? Error using ==> mupadmex mupadmex requires one string argument.

Error in ==> mupadengine.mupadengine>mupadengine.evalin at 115 [result,status] = mupadmex(statement,8);

Error in ==> solve at 99 [t,stat] = evalin(symengine,vc,'char');

Error in ==> my_flow_convps_C at 190 answer=solve(u+1,v-1);

However, when I used the same code in the command window, it works.

Just for the record u+1,v-1 isn't what Im actually solving, it was me trying to debug.

Thanks,

Chris