I am not sure what "unable to maintain stores" means but regarding Sales Orders from CRM, if you are using CRM Quick Order Entry and Sage's Sage 100 integration (not a 3rd party integration) then the issue could be the Tomcat port in IIS URL Rewriter Rule.

I would recommend viewing Sage Knowledgebase Articles 57398 "Error "502 - Web server received an invalid response while acting as a gateway or proxy server." in Quick Order Entry after upgrading from Sage CRM 7.2 to Sage CRM 7.3." or 71718 "Error: "502" Gateway Error in CRM Quick Order Entry on HTTPS connection for external users in CRM 7.2" on the Sage Portal https://support.na.sage.com.

Here is the resolution from the first article to change the port to the correct port in IIS:
Go to IIS Manager.
Select Default Web Site.
In the Feature View, IIS section, click URL Rewrite.
Select the rule for RWC ‘sage100erp_rwc’ and click the ‘Edit’ action
Scroll to the bottom of the edit window to the section defining the Rewrite action
Change the port number to the value used for the CRM instance (default is 10009)
If you do not know the port, execute the following query in SQL Server Management Studio for the CRM instance:
select parm_name, parm_value from custom_sysparams where parm_name='CRMTomcatPort'
Save changes
Restart IIS and Tomcat service

I am not sure what "unable to maintain stores" means but regarding Sales Orders from CRM, if you are using CRM Quick Order Entry and Sage's Sage 100 integration (not a 3rd party integration) then the issue could be the Tomcat port in IIS URL Rewriter Rule.

I would recommend viewing Sage Knowledgebase Articles 57398 "Error "502 - Web server received an invalid response while acting as a gateway or proxy server." in Quick Order Entry after upgrading from Sage CRM 7.2 to Sage CRM 7.3." or 71718 "Error: "502" Gateway Error in CRM Quick Order Entry on HTTPS connection for external users in CRM 7.2" on the Sage Portal https://support.na.sage.com.

Here is the resolution from the first article to change the port to the correct port in IIS:
Go to IIS Manager.
Select Default Web Site.
In the Feature View, IIS section, click URL Rewrite.
Select the rule for RWC ‘sage100erp_rwc’ and click the ‘Edit’ action
Scroll to the bottom of the edit window to the section defining the Rewrite action
Change the port number to the value used for the CRM instance (default is 10009)
If you do not know the port, execute the following query in SQL Server Management Studio for the CRM instance:
select parm_name, parm_value from custom_sysparams where parm_name='CRMTomcatPort'
Save changes
Restart IIS and Tomcat service