Yes the DictEdit might fail if the list it's trying to display is huge - it's trying to display all items in that listbox on the dialog.
To find out which thing has a lot of items, I'd go with MP's routine (as Lee's linked to in post #12). From that you should be able to pick up what the dictionary name is, then use Kruuger's idea to remove the dictionary - you should then be able to purge normally.
E.g. running the Counts command from MP's routine:...
Dictionaries.Count = 14
ACAD_CIP_PREVIOUS_PRODUCT_INFO has no <Count> property.
ACAD_COLOR.Count = 0
ACAD_DGNLINESTYLECOMP.Count = 21135
Groups.Count = 0
Layouts.Count = 3
Nameless, Handle=72.Count = 3
ACAD_MLEADERSTYLE.Count = 2
ACAD_MLINESTYLE.Count = 1
PlotConfigurations.Count = 0
ACAD_PLOTSTYLENAME.Count = 1
ACAD_SCALELIST.Count = 33
ACAD_TABLESTYLE.Count = 1
ACAD_VISUALSTYLE.Count = 24
AcDbVariableDictionary.Count = 7
DimStyles.Count = 3
Groups.Count = 0
Layers.Count = 1
Layouts.Count = 3
Linetypes.Count = 2173
RegisteredApplications.Count = 8
Modelspace.Count = 1
Paperspace.Count = 0
Again, as Kruuger's mentioned earlier ... simply remove the offending dictionary:(dictremove (namedobjdict) "ACAD_DGNLINESTYLECOMP")
And for the 2nd version:Command: COUNTS
Blocks.Count = 4
*Model_Space.Count = 0
*Paper_Space.Count = 2
EC_TICK.Count = 3
EC-Arrow.Count = 1
Dictionaries.Count = 29
ACAD_BACKGROUND.Count = 0
ACAD_CIP_PREVIOUS_PRODUCT_INFO has no <Count> property.
ACAD_COLOR.Count = 1
Nameless, Handle=24D6DA has no <Count> property.
Groups.Count = 0
ACAD_IMAGE_DICT.Count = 1
Nameless, Handle=29399 has no <Count> property.
Layouts.Count = 2
Nameless, Handle=10.Count = 3
ACAD_MLEADERSTYLE.Count = 1
ACAD_MLINESTYLE.Count = 1
PlotConfigurations.Count = 26
ACAD_PLOTSTYLENAME.Count = 1
ACAD_SCALELIST.Count = 86
ACAD_TABLESTYLE.Count = 1
ACAD_VISUALSTYLE.Count = 26
AcadDim has no <Count> property.
AcDbVariableDictionary.Count = 11
ADS_HISTORY.Count = 1
AEC_CLASSIFICATION_SYSTEM_DEFS.Count = 0
AEC_DISP_REP_CONFIGURATIONS.Count = 5
AEC_DISP_REP_SETS.Count = 10
AEC_DISP_REPS.Count = 151
AEC_DISPLAY_PROPS_DEFAULTS.Count = 142
AEC_LAYERKEY_STYLES.Count = 3
AEC_PROPERTY_SET_DEFS.Count = 0
AEC_VARS.Count = 3
ASE_INDEX_DICTIONARY.Count = 1
BNS_VARIABLES.Count = 1
DimStyles.Count = 2
Groups.Count = 0
Layers.Count = 3
Layouts.Count = 2
Linetypes.Count = 3
RegisteredApplications.Count = 10
Modelspace.Count = 0
Paperspace.Count = 2
However, a straight open and save reduces that particular file from 5.5MB to 206kB. Those AEC dictionaries are usually from some vertical product like ACA - thus ACad generally fixes issues on these with a simple open & save.
If I further use my DictEdit or follow Kruuger's idea to remove all AEC (and such), then do a purge regapps and all that, the file furthe4r reduces in size to 132kB.
It might be that those entities (e.g. the purge RegApps show some others removed) are using custom ARX objects. You might need to download the object enablers from ADesk:Command: -PU
-PURGE
Enter type of unused objects to purge
[Blocks/Dimstyles/Groups/LAyers/LTypes/MAterials/MUltileaderstyles/Plotstyles/SH
apes/textSTyles/Mlinestyles/Tablestyles/Visualstyles/Regapps/Zero-length
geometry/Empty text objects/All]: r
Enter name(s) to purge <*>:
Verify each name to be purged? [Yes/No] <Y>: n
Deleting registered application "ACAD_MLEADERVER".
Deleting registered application "AcAecLayerStandard".
Deleting registered application "AECBASE".
Deleting registered application "DCO15".
Deleting registered application "REVIT".
5 registered applications deleted.