I just encountered this issue after installing WordPress on one of my clients’ shared hosting (1and1).
I personally like 1and1’s control panel and actually this is almost the only problem I have with them.
But it looks that they got a bit greedy with their resources and would offer you by default just a bit of memory to use.
Luckily there’s a solution for that. It looks like if you create a text file named php.ini in the directory “/wp-admin/” within your WordPress installation,
you’ll convince your php instance to use more memory.
Oh, inside the file just enter “memory=20MB” and then upload it. Good luck!