During my lab I have often a crash of my router C3725 and it's really annoying.

The router doesn't responding anymore (CLI), so I turn off and turn on the node but after I have often this error :
% There may not be enough space available to collect the complete crashinfo
% It would be advisable to have 280755 bytes free space on flash:crashinfo
[….]
Router#show flash:
System CompactFlash directory:
File Length Name/status
1 660 vlan.dat [deleted]
2 720 vlan.dat
[134217724 bytes used, 0 available, 134217724 total]
131072K bytes of ATA System CompactFlash (Read/Write)
I don't understand why and how to fix it.
Please could you help ?