Hi, I got the answer for this. Try this, it may work for you also.
When you browse the Report Manager, you're getting the above error message.
To resolve this issue, Do the following,
Search for the key
---- MaxActiveReqForOneUser in RSREPORTSERVER.config file under the ReportServer directory,
And set the value to 400 that would look like this
Save the rsreportserver.config file and restart the IIS
Specifies the maximum number of simultaneous and in-progress connections that a single user can open to Report Manager. Once the limit is reached, further connection requests from the user are denied. This configuration setting is intended to mitigate a denial of service attack.
Valid values are 0 to a maximum integer. 0 indicates no limit on the number of connections. The default is 20.
Note that most requests process very quickly so it is unlikely that a single user will have more than 20 open connections at any given time. If users are opening more than 15 process-intensive reports at the same time, you might need to increase this value.