The filesystem specified after the first colon probably contains many small files, exceeding the per-filesystem limit for inodes (file information nodes).
If many small files were created unintentionally, removing them resolves the problem.
Otherwise, follow these steps to increase filesystem capacity for small files. Make several backup copies of the filesystem on different tapes (for safety), then bring the machine down to single-user mode. Use the newfs(1M) command with the -i option to increase inode density for this filesystem. Here is an example:
# newfs -i 1024 /dev/rdsk/partition |