I am unable to connect with the unit when it is plugged into a Cisco SLM 224P switch.

According to Dell:

Flow Control Support (IEEE 802.3X): Flow control enables lower speed devices to communicate with higher speed devices by requesting that the higher speed device refrains from sending packets. Transmissions are temporarily halted to prevent buffer overflows. For information on configuring Flow Control for ports or LAGs, see “Defining Port Configuration” or “Defining LAG Parameters” in the Dell™ PowerConnect™ 35xx Systems User’s Guide.

Change to MDI:

MDI / MDIX ­ displays the Media Dependent Interface (MDI) / Media Dependent Interface with Crossover (MDIX) status on the port. Hubs and switches are deliberately wired the opposite of the way end stations are wired, so that when a hub or switch is connected to an end station, a straight through Ethernet cable can be used, and the pairs are matched up properly. When two hubs or switches are connected to each other, or two end stations are connected to each other, a crossover cable is used to ensure that the correct pairs are connected. The possible field values are: – MDIX ­ Use for hubs and switches. – MDI ­ Use for end stations.