Sachin,
The acknowledge upload message is a little mis-leading. I was having a
similar problem and didn't understand why mobilink kept sending this,
I thought it was just hanging for some unknown reason.
I ran the mobilink monitor and realized that mobilink would send this
message repeatedly while running my download cursor scripts, so really
a more accurate message might be "Compiling download data" or
something to that affect.
Turns out one of the queries I implemented for a download cursor was
poorly written and took a long time to execute. I rewrote the query
and the sync goes much faster. So, long story short, take a look at
your mobilink download_cursor scripts and make sure your queries are
optimized.