Hi Daniel,
You may want to open a support ticket to get specific help, but in general the below steps have helped me troubleshoot similar situations:
1) More specific permissions always override more general permissions
a) type permissions override project permissions in Integrity
b) archive permissions override devpath perrmissions which override project permissions which override global permissions in Source
c) user permissions override group permissions
2) If there are conflicting permissions at the same level, "Deny" overrides "Allow" which overrides "Blank"
What this means is that if the user is in 2 groups, one with "Allow" and one with "Deny", the "Deny" will take precedence.
The other thing to keep in mind (but it may not be relevant, because the error message will be along the lines of "policy prevents creating a change package" instead of the "permission is denied" that you mentioned) is that Change Packages are enabled on each type for a specific set of States and a specific set of users, based on how you configure the "Change Packages" section of the Type in the administrator client.
Most of our errors around this happen because the item is in the wrong State for open change packages or because the user is not part of the proper group or in the proper field for it to be allowed.
Hope that helps,
Matt
