Yes, PPTP and IPSec can co-exist.
The reason they are failing to do so could depend on configuration.
If you want, I can take a look at your configuration. It is not advised to upload it to this forum. However, if you want, you can email it to me.
Could you elaborate on what you mean by a single ACL group being referenced by both PPTP and IPSec?
It the PPTP clients are able to connect but not pass traffic, then apparently GRE is not working. What device are you using to terminate the VPN tunnels?
Paras