gre tunnel going up and down all the time

[lohelle]

I have a problem with a GRE tunnel going up and down all the time. When it is up I can reach all my resources on the external network, but when it is down I can of cource not reach them..

router1:
ethernet 1/0 is the wan interface with public ip 200.200.200.2
ethernet 0/0 is the local interface with ip 10.0.0.1
interface Tunnel1
ip address 192.168.70.1 255.255.255.252
keepalive 10 10
tunnel source Ethernet1/0
tunnel destination 201.201.201.2

ip route 10.0.1.0 255.255.255.0 192.168.70.2

router2:
fastethernet 1/0 is the wan interface with public ip 201.201.201.2
fastethernet 0/0 is the local interface with ip 10.0.1.1
interface Tunnel1
ip address 192.168.70.2 255.255.255.252
keepalive 10 10
tunnel source Ethernet1/0
tunnel destination 200.200.200.2

ip route 10.0.0.0 255.255.255.0 192.168.70.1


the tunnel is up 10-15 sec and then goes down for a minute or two.. and then goes up again (etc). I think the intervals are the same all the time (but it is down longer than it is up)

Router1 is a 2610 with 16MB flash and 64MB memory running c2600-advsecurityk9-mz.124-3.bin

router2 is a 2610XM with 32MB flash and 192MB memory running c2600-adventerprisek9-mz.124-7.bin

Everything is stabe except for the GRE tunnel.

Any suggestions??