Simple explanation. Ping/traceroute from the location with the rejects.  I suspect you have high latency/bad Internet. Rejects tend to come from things like bad internet.

Also try a different data center for the pool you use. Most pools have more than one datacenter. One may be closer to you.  

In windows open a CMD prompt as admin.

type "ping your.pool.address"

Should spit out some numbers if any are 100ms+ that's bad.

For example:


You can also run traceroute.  In windows the command is:


Traceroute shows you every individual hop between you and your pool. Each hop will show how many milliseconds it takes for that hop. The higher the number the worse your connection to the pool.  Often times you have to go through one slow internet hub that slows down your whole connection.

Traceroute will also show you how many hops between you and your pool. The more hops the worse your connection will be. 10 is probably ok but 20 means you're more likely to have more bad connections between you and the pool.

If you use a different datacenter or pool you just change that part of the code.