The Load Combination and Analysis is a very memory intensive process.  If you have too many loads you should try reduce them so that # of generated loads is less and in turn the analysis will run better.  Here are some steps that may help.

One of the few changes you can try with the model so it created less load combinations are:

• When you generate loads for load type L+ln try to limit the number of trucks, if possible limit the loaded lanes to "3 lane loaded" and then generate the loads. These changes will help in creating less number of selected load types.  Also use Constant Spacing instead of Variable spacing.
• Application of wind on structure/live need not be applied at every 15 degrees instead apply at every 30 degree this will eventually reduce the number of load combinations drastically.
• If you have breaking force generated with live load, please delete all the Braking forces and just leave one braking force BR1 and then generate the load combinations.  Since braking force and Live load are related , Please click on the combination option, click on Parameter option and then select Dependent Load case combinations and then click on Dependency Table and in the new window select BR option and then select NONE from the drop down menu.

• With the Load combination groups, I don't know if it is required to select all the load Groups for analysis.  According to AASHTO all the load combinations may not apply for a single case using certain discretion try to select only the required load groups.
• Finally try to generate all the load combinations by selecting "Dependent load case combinations" instead of cross combinations.  If “Dependent Load case” combinations doesn't work then use cross combination and run the program.