I am assuming you are returning JSON?
You can adjust the JSON response size in the web.config with:
<configuration>
<system.web.extensions>
<scripting>
<webServices>
<jsonSerialization maxJsonLength="1000000" />
</webServices>
</scripting>
</system.web.extensions>
</configuration>
Doing a quick search, it looks like the default size is 102400.
maxJsonLength Optional attribute.
Configures the maximum length of the
JSON string (the maximum number of
UTF-8 characters).
The default length is 102400.
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