+++ This bug was initially created as a clone of Bug #716484 +++

Description of problem:
If regular available subscriptions for a particular child channel are 0, trying to subscribe flex guests to that child channel through System Set Manager fails with an Internal Server Error

Also if there was 1 regular subscription available for that child channel and when you select more than 1 flex guest systems to subscribe to that child channel, it just subscribes 1 system to that child channel and skips the remaining systems.

Version-Release number of selected component (if applicable):
RHN Satellite v5.4.1

How reproducible:
Always

Steps to Reproduce:
Prerequisite:
Satellite with fewer regular entitlements and more flex guest entitlements.
Example:
1 regular and 7 flex


1. Register 1 regular system and 2 flex guest systems on Satellite
2. Subscribe the regular system to RHN Tools channel
3. Select the 2 flex systems -> System Set Manager -> Channel -> select RHN Tools channel -> select subscribe and click on Alter Subscriptions
  
Actual results:
Fails with an ISE

Expected results:
It should subscribe the system to RHN Tools channel as there are 7 flex subscriptions available for it

Additional info:
This issue is very much similar to https://bugzilla.redhat.com/show_bug.cgi?id=673394 . But in bz#673394 we were unable to system system manually through alter channel subscription and in the current case we can't subscribe systems through system set manager.