Memory allocation errors are due to your Operating System not having the resources to allocate any more memory for the simulation.
Below are a couple of things that you can do to avoid the memory allocation errors in Simulink:
1. Turn off the Workspace I/O (to do that, in the Simulink model go to Simulation=>Parameters=> Data Import/Export and uncheck the time and output boxes).
2. Increase the step size of the simulation
3. Reduce the length of the simulation
4. Increase the virtual memory of your computer (right click on the My Computer Icon, go to Properties and choose Performance).
5. Memory requirements of running a model depends on many factors such as the size of model, the signal size, memory usage by the user defined S-functions, etc.
Depending on the requirements of your simulation, you might consider increasing your physical RAM memory or switching to 64-bit machine since they support considerable large amount of memory as compared to 32-bit machines.
For other options on improving simulation performances you may refer to the Simulink User's Guide. If you do not have the manual you can use the online version at:
You may also refer the Technical Note on Memory Management in Simulink, at the link below: