What is the large different between fixed DD ambiguity yield from Ski and float DD ambiguity that computed.

I process leica SR299 receiver observation with ski software version
2.3 and obtain these results
Rover coordinate
X=3529710.548;
Y=4330981.661;
Z=3066093.621;
Ambiguity values
Reference satellite : 28/L1 
Satellite number 
8   7    29    27    10     26
DD  Ambiguity values is respectively           
8   6   -49    32   102     54

Then by use of reference and above  rover station coordinate and
precise ephemeris I compute DD distance between receiver and satellite
 and with L1 phase observation compute DD phase L1
As respect baseline length is very short ( 277 cm ) we can ignor any
error and bias and can calculate DD float ambiguity
 As a result DD flout ambiguity value is 

Reference satellite : 28/L1 
Satellite number 
8    7      29     27   10     26
DD float Ambiguity values
-5.599   -4.911    -63.31   19.537    89.756  38.899

What is the large  different between fixed DD ambiguity yield from Ski
and float DD ambiguity that computed.
 
Please help me to solve this problem