The only option that that the SRM AIM has control over that might cause a Web Server to return the 403 Forbidden error is the "User Agent String". As the SRM AIM is java based, the default User Agent String for SysEDGE/SRM 5.9 is "Java/1.7.0_72". It is possible to block requests based on the User Agent.
To set the SRM's User Agent to something different, edit the \port(161|1691)\plugins\svcrsp\svcrsp.cf file on the SRM AIM system and uncomment the following line by removing the "#":
# Uncomment to override the default UserAgent string used in HTTP tests
#useragent="Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 7.1; Trident/5.0)"
should then become:
useragent="Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 7.1; Trident/5.0)"
If the sample User Agent that is provided in the svcrsp.cf is still not acceptable, this can be modified to a different value. For example (Firefox 55 64 Bit, running on Windows 10 64 Bit):
useragent="Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:55.0) Gecko/20100101 Firefox/55.0"
Once the file has been modified, save it and restart the SystemEDGE agent for the new value to be picked up.
Note: If this does not resolve the problem, you may want to check with the web server admin to confirm why the 403 is being returned and/or open a support case with CA Support.