Memory issues & jobs hanging

We are staring to expeience jobs "hanging", meaning they get stuck on a data flow. The hanging happens on different data flows and tables during our nightly loads. Here is a sample of the last two Trace statements before it hung.

(11.7) 09-30-08 08:40:26 (8128:5284) DATAFLOW: Cache statistics determined that data flow <TableXYZ> uses <0> caches with a total size of <0> bytes. This is less than(or equal to) the virtual memory

<1606418432> bytes available for caches. Statistics is switching the cache type to IN MEMORY. (11.7) 09-30-08 08:40:26 (8128:5284) DATAFLOW: Data flow <TableXYZ> using IN MEMORY Cache.

Any ideas what we are doing wrong?