recently i buy Nexus 9K virtual lab and when i try to access nexus switch1 some time  it's goes in this mode (loader>).

how to fix this 

yes i am also heaving same problem with nexus switch. but if you can see the instruction they clearly mention that if your nexus switch goes into Loader> then run the command (loader > boot bootflash:nxos.7.0.3.I7.6.bin). it's work for me. you can try the same

yes if any one follow the instruction step by step which is given on lab. i think no one can get any challenges to build the Nexus lab.

the instruction is very simple and very helpful. i enjoyed with this Nexus lab a lot

I also faced the same issue but instructions are easy to follow.  Later on I also build my own nexus 9k lab on a server and this issue occurs on that as well. I used the uninets nexus workbook for practice various scenarios but it does not have VDC labs. Can anyone of you suggest if it is possible to do VDC lab on my virtual nexus lab. 

Now I am getting a different issue. I am using firebox, the lab page is not opening and I keep redirecting to the main page. Other sample labs are opening without any issues.