B&R PLCs go into service mode when something goes wrong (divide by zero, cycle time violation, page fault, etc) or as an option when doing a major transfer (updating firmware, re-transferring the entire project, etc). You get out of service mode by doing a warm restart (assuming whatever error condition isn't still going on).
To see what has put you in service mode, you can open the logger in either Automation Studio (in the 'Open' menu) or in SDM, which is the web based System Diagnostics Manager that the PLC is hosting at http://<PLC_IPaddress>/sdm (yes, it still works in service mode). The most common way to get into service mode is a cycle time violation, which comes from your code taking too long (normally because you're stuck in a loop or calling File IO functions in a fast task class). Page faults are essentially memory leaks in your code where you are copying data beyond the bounds of the variable you think you are writing to (writing 100 characters to a 10 character string or going beyond the bounds of an array). Divide by zero is pretty self explanatory.
You can search the help for any error number you see in the logger and you can also use the backtrace feature in the logger to see what part of your code cause the problem. You can also get free phone support from B&R or your distributor. Since you're in Milwaukee, they have an office in Chicago and, Mequon north of Milwaukee and the US headquarters in Atlanta that could all help (support line is open till 6PM EST in ATL and other offices till 5PM).